Free Technical Calculators & Engineering Tools
Accurate calculators for electrical, HVAC, mechanical and solar work — every tool shows its formula, a worked example, its assumptions and its limitations. No fluff, no sign-up.
Browse by category
Electrical
18 toolsFree 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.
HVAC & Climate
13 toolsFree 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.
Mechanical Engineering
16 toolsFree 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.
Solar, Energy & Batteries
10 toolsFree 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.
Design guides
How each discipline's calculations fit together — load, conductor, protection, economics — with the right calculator at every step.
Why IngCalc is different
Most calculator sites give you a number and nothing else. Every tool here documents the model it uses — the exact formula, the standard or reference behind the constants, the assumptions baked in, and the cases where the result will be wrong. You can defend the numbers you get here in front of a client, an inspector or a professor.
The library grows by category: complete clusters of related tools (wire sizing connects to voltage drop, which connects to motor current) rather than isolated one-off calculators.
How tools are developed
Each tool starts from a real, recurring technical question. The calculation model is separated from the page as pure math with documented inputs and outputs. Constants come from named sources — NEC conductor tables, ASHRAE methods, ISO standards, NREL data. Every engine is verified against reference values with automated tests before publication.
See the About page for the full development process, or meet the author.