Engineering tools

Free engineering tools

Calculators and utilities we use in our own engineering work, published free. Every tool shows its formula, assumptions, a worked example and its limitations, so you can check the result by hand.

These tools run entirely in your browser; nothing you enter is sent to us. They are engineering aids, not a substitute for the applicable standard or a qualified engineer's sign-off.

Electrical

Calculators for cable sizing, voltage drop and everyday low-voltage installation questions, with the formulas and limits behind them.

Calculate voltage drop and percentage drop for DC, single-phase and three-phase circuits from cable length, current, conductor size and material, and find the smallest conductor that meets your limit.

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Energy

Calculators for battery backup, UPS and inverter sizing and energy budgeting, with the assumptions each one makes spelled out.

Battery backup runtime calculator

Estimate how long a battery bank will run a load through a UPS or inverter, and the capacity needed for a target runtime, accounting for depth of discharge and inverter efficiency.

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How we build these tools

Each calculator is a small, self-contained script with its inputs, units and formula defined in code and reviewed like any other engineering deliverable. When we correct or extend a tool, the page notes the date of the last review. If you spot an error, tell us; we would rather fix it than have someone size a cable wrongly.