All Technical Calculators & Tools
57 free calculators across four engineering sectors. 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.
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 a copper circuit — 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, hours per day and your rate to get daily, monthly and yearly energy and cost — the standard appliance running-cost calculation.
- 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.
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.
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.
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 — 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.
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.