Free Engineering Calculators
18 free online engineering calculators covering electrical circuits, mechanical systems, automotive engineering, chemistry and thermodynamics. From Ohm's law and voltage drop to BTU, gear ratio, molarity and wind chill — every tool explains the formula it uses and runs entirely in your browser.
About engineering calculators
Engineering calculations usually involve a formula you already know — the challenge is applying it correctly with the right units and the right constants. The tools on this page handle the arithmetic, unit conversions and rounding so you can focus on the engineering decision, and every calculator shows the formula it uses plus a worked example you can compare against your own numbers.
The library covers four areas: electrical engineering (Ohm's law, voltage drop, power, resistor colour codes, battery runtime, electricity cost), mechanical and automotive (BTU, horsepower, engine displacement, gear ratio, fuel cost, gas mileage), chemistry (molecular weight, molarity, half-life) and environmental thermodynamics (wind chill, heat index, dew point). Where relevant, conversions use SI base units and reference values from recognised standards.
These tools provide general-purpose estimates based on standard formulas. Always verify critical values against applicable codes, standards and professional engineering guidance. Do not use them as the sole basis for design decisions involving safety or regulation.
Electrical Engineering
Circuits, wiring, resistor colour codes and energy usage.
Ohm's Law Calculator
Solve for voltage, current, resistance or power using Ohm's law.
Voltage Drop Calculator
Estimate voltage drop in a wire run given current and gauge.
Electrical Power Calculator
Compute electrical power in watts from voltage and current.
Resistor Color Code Calculator
Decode 4, 5 and 6-band resistor values from their colours.
Battery Runtime Estimator
Estimate battery runtime from capacity and device current draw.
Electricity Cost Calculator
Estimate electricity cost from power, hours and energy price.
Mechanical & Automotive
Engine, gearing, HVAC, fuel and thermodynamics tools.
BTU Calculator
Estimate BTU requirements for heating or cooling a room.
Horsepower Calculator
Convert torque and RPM into horsepower and kilowatts.
Engine Displacement Calculator
Compute engine displacement from bore, stroke and cylinder count.
Gear Ratio Calculator
Compute gear ratio and output speed from driver and driven gears.
Fuel Cost Calculator
Estimate trip fuel cost from distance, efficiency and price.
Gas Mileage Calculator
Compute fuel efficiency in mpg, km/L or L/100 km.
Chemistry, Physics & Environment
Molecular weight, molarity, half-life and atmospheric thermodynamics.
Molecular Weight Calculator
Compute molar mass from a chemical formula.
Molarity Calculator
Compute molarity, moles or volume from the other two values.
Half-Life Calculator
Compute remaining quantity, half-life or elapsed time.
Wind Chill Calculator
Compute wind chill from temperature and wind speed.
Heat Index Calculator
Estimate apparent temperature from heat and humidity.
Dew Point Calculator
Compute dew point and relative humidity relationships.
Related Guides
Understand the science behind the tools before applying them.
Engineering Calculator FAQs
Given any two of voltage (V), current (I), resistance (R) or power (P), the Ohm's law calculator solves for the remaining two using V = IR and P = VI along with their derived forms.
The voltage drop calculator covers standard AWG gauges from 0000 down to 40, plus metric equivalents. Copper and aluminium conductors are both supported, and results are compared against typical NEC percentage limits (3% branch, 5% total).
Displacement = π / 4 × bore² × stroke × number of cylinders. The engine displacement calculator accepts bore and stroke in mm, cm, inches or litres, and reports the result in both cc and litres.
They provide useful estimates and are suitable for preliminary calculations, homework and quick checks. For safety-critical, regulated or design-grade decisions, always verify results against applicable codes, standards and professional engineering judgement.
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