All Technical Calculators & Tools
113 free calculators across 8 engineering disciplines. Every tool documents its formula, assumptions, limitations and a worked example — designed for practitioners who need to understand the result, not just see a number.
Find a calculation by name, application or engineering discipline.
Electrical
Free electrical calculators: voltage drop, wire sizing, Ohm's law, kVA to amps, power factor correction and motor current. Metric and AWG, with formulas and examples.
- Voltage Drop CalculatorFind the voltage drop in single-phase and 3-phase circuits — absolute volts, percentage, final load voltage and heat loss. Uses NEC Chapter 9 Table 8 conductor resistances.
- Wire Size CalculatorPick the smallest standard copper conductor whose ampacity covers your load current, with the ampacity margin, metric cross-section and the code caveats that apply.
- Ohm's Law CalculatorLeave exactly one field blank and the calculator solves it from the other two — and shows power as a bonus. The classic V = I × R with all its rearrangements.
- kVA to Amps CalculatorEnter power as kVA, kW or hp and get the current for single or three-phase, with the kW/kVA conversion made explicit and the formulas documented.
- Power Factor Correction CalculatorEnter load kW, current PF and target PF to get the capacitor bank size in kVAR, the kVA capacity you free up and how much line current drops.
- Motor Current CalculatorEnter motor hp, voltage, efficiency and power factor to estimate full-load current — with the formulas, and clear notes on when to use NEC tables instead.
- Wire Resistance CalculatorFind the electrical resistance of any copper or aluminum conductor from the AWG table — round trip and per-unit-length values for voltage drop math.
- Electricity Cost CalculatorEnter device watts and hours per day (or metered kWh) plus your electricity rate ($/kWh) to calculate daily, monthly, and yearly appliance running costs.
- Transformer Sizing CalculatorEnter load kW, PF and voltages to get the required kVA with margin, plus primary and secondary currents for protection sizing.
- Three-Phase Power CalculatorEnter line voltage, current and PF to get kW, kVA and kVAR for a balanced three-phase load — the full power triangle.
- Voltage Divider CalculatorEnter Vin, R1 and R2 to get the divider output, its current draw and the power dissipated in each resistor — plus the loading caveats that matter in practice.
- Resistor Color Code CalculatorPick the four band colors to read the resistance value, tolerance and min/max range of any 4-band resistor.
- LED Resistor CalculatorEnter supply voltage, LED forward voltage and current to get the resistor value, its power rating requirement and the nearest standard values to buy.
- EV Charging Time CalculatorEnter battery kWh and charger kW to get charging time, grid energy drawn (including losses), range added and cost — for Level 1 through DC fast.
- Generator Size CalculatorAdd up your running loads and the biggest motor surge to get the minimum generator rating — with the sizing logic that prevents nuisance shutdowns.
- Wire Derating CalculatorEnter table ampacity, ambient temperature and conductor count to see the effective ampacity after NEC temperature and fill derating.
- Breaker Size CalculatorEnter the load current and whether it's continuous to get the design current and the next standard breaker rating — plus the conductor requirement that goes with it.
- Cable Reactance CalculatorFor large conductors where reactance matters: enter size and length to get R, X, Z and the AC voltage drop — the refinement over DC-only drop math.
- Parallel Resistor CalculatorEnter two or more resistor values to get the parallel equivalent — always smaller than the smallest branch, with the conductance sum shown.
- Capacitor Energy CalculatorEnter capacitance and voltage to get stored energy in joules and Wh, plus charge in coulombs and mAh — the numbers behind flash circuits and supercapacitor backup.
- Reactance CalculatorPick component type, enter the value and frequency, and get the reactance in ohms — the AC 'resistance' of inductors and capacitors.
- Series Resistor CalculatorEnter two or more resistor values to get the series equivalent — a straight sum, with the biggest resistor's voltage share shown.
- Current Divider CalculatorEnter total current and both branch resistances to get each branch's current — remembering the 'opposite resistor' formula that trips everyone once.
- RC Time Constant CalculatorEnter R and C to get τ, the practical 5τ settle time, the voltage at any instant, and the time to any target — the exponential that governs delays and filters.
HVAC & Climate
Free HVAC calculators: cooling and heating BTU load estimates, round duct sizing with friction loss, CFM and air changes per hour, plus SEER, EER and COP conversions.
- BTU CalculatorEstimate how many BTU/h your room needs for cooling, based on floor area with documented adjustments for climate, insulation, sun, people and appliances.
- Heating Load CalculatorSize a heater from floor area, indoor-outdoor design temperature difference and envelope insulation quality, with the U-factor model documented.
- Duct Size CalculatorEnter airflow and your design friction rate to get the round duct diameter, the next nominal size up, and the resulting air velocity — with the ASHRAE equation documented.
- Airflow / ACH CalculatorEnter room volume and target air changes per hour to get the required airflow in CFM, L/s and m³/h — or verify the ACH an existing fan delivers.
- SEER / EER / COP ConverterEnter a SEER rating to see the equivalent EER, COP, kW per ton and tons per kW — with an explanation of what each rating actually measures.
- Dew Point CalculatorEnter air temperature and relative humidity to get dew point, wet bulb and a straight comfort read — dew point, not RH, is the real comfort metric.
- Duct Velocity CalculatorEnter airflow and duct diameter to get velocity and friction rate — the companion check to the duct sizing calculator for existing systems.
- AC Running Cost CalculatorEnter your AC size in tons, its SEER and your runtime to get monthly and seasonal cost — the numbers that decide whether a SEER upgrade pays.
- Heat Index CalculatorEnter temperature and humidity to get the heat index and its health risk band — the same formula behind US heat warnings.
- Wind Chill CalculatorEnter temperature and wind speed to get the wind chill and how quickly frostbite can develop — the official US weather service formula.
- Degree-Day Heating CalculatorEnter heating degree-days, your home's UA (heat-loss coefficient) and fuel details to get seasonal fuel consumption and cost — the standard degree-day method.
- Sensible Heat & Airflow CalculatorWork with the core air-side equation Q = 1.08 × CFM × ΔT: enter two values to get the third, with metric conversions and typical target airflows.
- Fan Laws CalculatorChange a fan's RPM and see exactly what happens to airflow, pressure and power — the affinity laws that justify variable-speed drives.
- Psychrometric CalculatorEnter dry-bulb temperature and RH to get the moist-air properties coil and load calculations need: humidity ratio (g/kg), enthalpy (kJ/kg dry air) and dew point — altitude corrected.
- Heat Pump COP CalculatorEnter HSPF, outdoor temperature and your rate to get the COP the heat pump actually delivers at that temperature, its derated capacity, and the cost per kWh of heat vs resistance.
- Temperature Conversion CalculatorEnter a temperature in any scale to get the other two exactly, with the absolute-zero guard and the ΔT conversion rule HVAC calculations actually use.
- Air Density CalculatorEnter temperature, altitude and RH to get air density and the correction factor that fan curves and the 1.08 equation quietly assume away.
Mechanical Engineering
Free mechanical calculators: gear ratio and RPM, torque to power conversion, bolt torque and preload, belt length and pulley sizing, tap drill sizes for metric and imperial threads.
- Gear Ratio CalculatorEnter driver and driven teeth to get the ratio, output speed and output torque — with the mesh efficiency and multi-stage notes spelled out.
- Torque to Power CalculatorEnter torque and rotational speed to get mechanical power in kW and hp, with the torque converted to lb·ft for imperial work.
- Bolt Torque CalculatorGet the tightening torque for a metric bolt from its size, grade and lubrication state — with the preload, stress area and K-factor assumptions documented.
- Belt Length CalculatorEnter both pulley pitch diameters and the center distance to get the belt pitch length in mm and inches, plus the speed ratio.
- Tap Drill CalculatorEnter the thread major diameter and pitch to get the tap drill at 75% thread, adjustable for other engagement percentages, plus the nearest real drill bit.
- Pulley RPM CalculatorEnter both pulley diameters and the driver speed to get the driven RPM and belt surface speed — with the V-belt speed limits flagged.
- Hydraulic Cylinder CalculatorEnter bore, rod diameter and system pressure to get extend and retract forces — the rod side is weaker, and this shows exactly by how much.
- Gear Geometry CalculatorEnter module and teeth to get the full set of spur gear dimensions — pitch, outside and root diameters, circular pitch and tooth depth.
- Metal Weight CalculatorPick a shape and material, enter dimensions, get the weight in kg and lb — with nominal densities and mill-tolerance guidance.
- Engine Displacement CalculatorEnter bore, stroke and cylinders to get total displacement in cc, liters and CID — plus each cylinder's swept volume.
- Compression Ratio CalculatorEnter swept volume and all clearance volumes (chamber, gasket, piston) to get the true static compression ratio — the number that decides fuel tolerance.
- Spring Rate CalculatorEnter wire diameter, coil outer diameter and active coils to get the spring rate — the classic k = G·d⁴/(8·D³·n) formula with manufacturability notes.
- Torque Wrench Extension CalculatorUsing a crowfoot or extension changes the effective lever length. Enter the target, wrench length and extension to get the corrected wrench setting.
- Pump Power CalculatorEnter flow, head and efficiency to get hydraulic power (water hp) and shaft power — the numbers for motor selection on any centrifugal pump.
- Chain Length CalculatorEnter both sprocket tooth counts, center distance and chain pitch to get the exact chain length — rounded to an even link count to avoid offset links.
- Bearing Life CalculatorEnter the bearing's C rating, the actual applied load and RPM to get L10 life — the standard (C/P)³ fatigue calculation for ball bearings.
- Cantilever Beam CalculatorEnter the tip load, length and rectangular section to get deflection (δ = PL³/3EI) and bending stress at the fixed end — with a utilization check against steel yield.
- Shaft Torsion CalculatorEnter shaft diameter and torque to get surface shear stress (τ = Tr/J), or leave torque blank to size the shaft from an allowable stress.
- Machine Efficiency CalculatorEnter input and output power to get efficiency percentage and the watts lost as heat — the number your cooling and energy bill both care about.
- Simply Supported Beam CalculatorEnter the center load, span and rectangular section to get midspan deflection (δ = PL³/48EI), max stress and support reactions — with a utilization check.
- Hooke's Law CalculatorEnter force, area and specimen length to get stress, strain and elongation — or add a measured elongation to compute the material's actual modulus.
- Power from Force CalculatorEnter the force you must overcome and the speed you move at to get the power — the first number in sizing any linear drive.
- Pulley System CalculatorEnter pulley diameters (and optional input RPM/torque) to get the ratio, output speed, belt-driven torque and the belt surface speed check.
Solar, Energy & Batteries
Free solar and battery calculators: daily panel energy from peak sun hours, battery runtime with depth of discharge, full off-grid system sizing and charge controller sizing.
- Solar Panel Output CalculatorEnter panel wattage and your location's peak sun hours to get realistic daily, monthly and yearly energy (kWh) — including the standard loss derate.
- Battery Runtime CalculatorEnter battery Ah and voltage, your load in watts, plus DoD and inverter efficiency, to get realistic runtime — not the naive Ah ÷ A figure.
- Off-Grid System CalculatorEnter your daily energy consumption and get the battery bank, solar array and inverter sizes needed — with every sizing factor (DoD, autonomy, derate) explicit.
- Charge Controller CalculatorPick the controller type and get the minimum amp rating — MPPT from array watts ÷ battery voltage, PWM from total Isc — with the NEC margin applied.
- Solar String Size CalculatorEnter panel electrical specs and string layout to check cold-temperature Voc against the inverter maximum — the check that protects your equipment.
- Battery Bank Size CalculatorEnter your daily energy need and design choices (DoD, autonomy) to get the bank size in Ah and kWh, plus how many battery blocks to arrange.
- Battery Charge Time CalculatorEnter battery Ah, charger amps and the charge window to get realistic charge time — including the C-rate flag that protects battery life.
- Solar Savings CalculatorEnter system size, sun hours, rates and cost per watt to get annual savings, simple payback and the 25-year figure — with the honest caveats listed.
- Solar Panel Tilt CalculatorEnter your latitude to get the optimal tilt for year-round, winter-biased or summer-biased mounting, with the correct azimuth direction.
- Solar Panel Count CalculatorEnter your energy target and local sun hours to get the required array Wp, the number of panels and the rough roof area needed.
- Energy Consumption CalculatorEnter watts and hours for five load groups to get your daily kWh — the load-list number every off-grid or backup system design starts from, translated to battery and array sizes.
- Inverter Sizing CalculatorEnter continuous and surge loads to get the minimum inverter VA rating — with the power-factor conversion and surge margin that prevent nuisance shutdowns.
- DC/AC Ratio CalculatorEnter array DC size, inverter AC rating and sun hours to get the DC/AC ratio and a screening estimate of how much energy clipping wastes at peak sun.
- PV DC Cable Loss CalculatorEnter string Vmp/Imp, one-way run and cable size to get the DC drop and the watts lost every peak hour — the 25-year tax of undersized PV cable.
Construction
Free construction calculators: concrete volume and mix ratios, CMU block and brick takeoffs, rebar weight, stud walls, stairs, roof pitch, gravel and asphalt tonnage — with formulas, waste factors and IRC/ACI checks.
- Concrete CalculatorEnter your pour dimensions and get the volume in cubic yards, the bag count for 80, 60 or 40 lb mixes, and the weight — with the 5% waste margin already applied.
- Concrete Mix Ratio CalculatorEnter the wet volume you need and the mix ratio; get cement bags, sand and gravel volumes, and the water for a 0.5 water-cement ratio — with the shrinkage factor shown.
- CMU Block CalculatorEnter wall dimensions and block size to get the CMU count with joints and breakage included, plus mortar bags, sand volume and the wall's weight for footing checks.
- Brick CalculatorEnter wall dimensions, brick standard and bond pattern to get the brick count with joints and waste included, plus the mortar volume in bags.
- Rebar Grid CalculatorEnter slab size, bar size and spacing to get bar counts, total length with laps, weight, and whether the spacing meets the ACI 0.0018 shrinkage minimum — with a spacing chart.
- Footing Size CalculatorEnter the column load in kips and the soil's allowable bearing in ksf to get the required footing area, snapped to practical dimensions, with the actual bearing pressure shown.
- Stud Wall CalculatorEnter wall dimensions and stud spacing to get the stud count with openings allowance, the cut length above the plates, plate lumber, board feet and sheathing sheets.
- Stair CalculatorEnter the total rise and target riser to get the full layout — riser count, actual riser height, run, stringer length — with IRC compliance and comfort checks built in.
- Roof Pitch CalculatorEnter the rise per 12 inches of run (and the footprint area) to get the pitch angle, percent grade, rafter factor and the true sloped roof area for shingles and sheathing.
- Board Foot CalculatorEnter nominal thickness, width, length and piece count to get board feet, total volume and cost — using the nominal-dimension convention hardwood is bought and sold by.
- Gravel CalculatorEnter the area and depth to get cubic yards, tonnage for the selected material (gravel, crushed stone, sand, topsoil, mulch), bag count, and the 10% order margin.
- Drywall CalculatorEnter room dimensions to get sheet count by size, board weight for delivery planning, joint compound gallons, tape rolls and screw weight — waste included.
- Asphalt CalculatorEnter area and compacted depth to get asphalt tons at 145 lb/ft³, the loose order quantity that accounts for compaction, and the square-yard figure paving quotes use.
- Excavation CalculatorEnter pit or trench dimensions to get the in-ground (bank) volume, the hauled (loose) volume with soil swell applied, and the truckloads disposal will need.
- Paint CalculatorEnter room dimensions and coats to get paintable area, gallons needed and gallons to buy — with the spread-rate reality of rough or unprimed surfaces.
- Tile CalculatorEnter floor area and tile size to get the exact tile count, the order quantity with pattern waste included, and the thinset and grout the job consumes.
- Ramp CalculatorEnter the rise to climb and your slope ratio to get the ramp's run, slope length, angle — and how many landings the rise forces.
- Cut & Fill CalculatorEnter pad size and the two elevations to get the cut or fill volume — plus the hauled (cut) or compacted (fill) quantity the site work actually moves.
- Drainage Runoff CalculatorEnter area, rainfall depth and surface type to get the runoff volume in gallons and litres — the rational-method logic for a single storm event.
- Lumber Weight CalculatorEnter nominal size, species and count to get the weight per board and the total — the number behind delivery payloads and floor loading checks.
Plumbing & Water
Free plumbing calculators: pipe velocity and sizing, Darcy-Weisbach pressure loss, water volume in pipes and tank capacity. Metric and imperial, with design velocity guidance.
- Pipe Flow CalculatorEnter flow and pipe size to get velocity and the verdict: good supply range, noisy, or hammer-and-erosion territory.
- Pipe Pressure Drop CalculatorEnter flow, size, length and material roughness to get head loss and pressure drop — the numbers that decide whether the far shower gets decent pressure.
- Pipe Size CalculatorEnter flow and your velocity ceiling (supply 2.4 m/s, hot 1.5, pump suction 1.2) to get the minimum bore and the next standard size up.
- Pipe Volume CalculatorEnter internal diameter and length to get the litres (or gallons) the pipe holds and what that water weighs — the number behind flushing volumes and recirculation design.
- Tank Volume CalculatorEnter internal dimensions to get capacity in L/gal, the weight of the water when full, and the barrel equivalent — before freeboard and outlets take their share.
Thermodynamics & Heat Transfer
Free thermodynamics calculators: wall conduction and U-value, thermal expansion, ideal gas law, sensible and latent heat, and heating power from flow — with sources and worked examples.
- Heat Conduction CalculatorEnter layer conductivities and thicknesses (up to three) plus area and ΔT to get the U-value, R-value and heat flow through the assembly.
- Thermal Expansion CalculatorEnter material, length and temperature swing to get the growth — the number expansion loops, pipe guides and bridge joints exist to absorb.
- Ideal Gas CalculatorEnter two of pressure/volume/temperature and the ideal gas law solves the third — with the Kelvin trap and unit conversions handled.
- Sensible & Latent Heat CalculatorEnter mass, material and temperature change to get sensible heat in kJ/kWh/BTU — with the freeze and boil latent heats of water shown for comparison.
- Heating Power CalculatorEnter flow and ΔT to get thermal power in kW, BTU/h and tons — with the hydronic shortcut (kW ≈ L/min × ΔT ÷ 14.3) built in.
CNC & Manufacturing
Free CNC and machining calculators: spindle RPM from cutting speed, table feed from chip load, cycle time, material removal rate and production planning.
- Cutting Speed to RPM CalculatorEnter surface speed and diameter to get spindle RPM — the first number every speeds-and-feeds calculation needs, in both metric and SFM.
- Feed Rate CalculatorEnter RPM, chip load and flutes to get feed in mm/min and IPM — the second number of every speeds-and-feeds pair.
- Machining Time CalculatorEnter cut length, feed rate and passes to get cutting time, total cycle and parts per hour — the basis of every machining quote.
- Material Removal Rate CalculatorPick the operation, enter the engagement figures, and get MRR in cm³/min and in³/min — the number that sizes the spindle power.
- Production Rate CalculatorEnter cycle time, shift length and availability to get parts per shift and the utilization percentage — the OEE-shaped reality check on capacity plans.
How to use these tools
Start with the category that matches your problem. Each tool includes a worked example with real numbers so you can verify the calculation against your own situation before relying on the result.
The About page explains how tools are developed, how formulas are sourced and how results are verified. If you find an error, report it — corrections are prioritized.