What we calculate
Our 19 tools cover relationships between electrical quantities, cable geometry, lengths and costs. They use the values you enter and the model described on each page. The formula, your substituted inputs and the scope accompany the result.
DC Ohm’s law is restricted to a positive, constant resistance. AC power conversions assume sinusoidal steady-state supply voltages and use RMS quantities and true power factor. Three-phase conversion assumes a balanced load and uses line-to-line voltage. Energy tools use entered operating time and a single entered rate.
Choose inputs that describe your calculation
Cable calculations use the dimensions or electrical properties you supply. Check the manufacturer’s data and the conditions it applies to: an outside cable diameter differs from its conductor diameter, and a voltage-drop coefficient must match the circuit arrangement.
Geometric area percentages describe areas. They do not establish a permitted fill level or whether cables can physically fit and be installed. Connected power is a sum of input ratings; maximum demand requires a separate assessment of how the equipment operates.
Numbers, rounding and invalid inputs
Calculations use decimal arithmetic with 100 significant digits internally. Results display up to eight significant figures, using half-up rounding. The approximately-equal symbol marks values rounded for display. Irrational values such as √3 and recurring quotients necessarily have finite numerical approximations. Display precision does not express measurement accuracy.
Blank values, non-numeric strings, negative input values, division by zero and unsupported modes produce no result. Positive inputs must fall between 0.000000001 and 1,000,000,000,000; some fields have narrower bounds. Power factor must be greater than zero and no more than one. Daily operating time cannot exceed 24 hours. Lamp counts and day counts must be whole numbers.
Zero is valid where meaningful, such as zero energy use or a zero tariff. The Ohm’s law tool requires positive inputs so that the requested quantities are determined. A negative LED saving is allowed as an output: it means the new lighting uses more energy.
How to use a result
Read the model before entering values. Use the specified units, check whether the power is electrical input or equipment output, and confirm that any phase assumptions apply. The example tariffs are illustrative values, not current market prices. The cost calculations exclude charges they do not explicitly include.
When copying a result, the tool includes the inputs, formula and assumptions. Changes to inputs clear the previous result so an old answer is not displayed beside new values.
References
- Fluke · Ohm’s law ↗
- Schneider Electric · Electrical Installation Guide ↗
- Virginia Tech · Estimating energy use ↗
- Eland Cables · Voltage drop ↗
- Fluke · 1670 series loop and fault-current measurements ↗
- NIST · Copper wire tables, Handbook 100 ↗
- Schneider Electric · Definition of reactive power ↗
- IET · BS 7671 and supporting guidance ↗
Sources accessed 4 September 2026. The IET is linked for current installation standards and guidance; its tables are not reproduced in our calculator engine.
If something looks wrong
Report the calculator, inputs, selected mode and expected result through our issue-report page. Include the source for the expected value where possible. Do not rely on a result you have reason to doubt.