This page explains the rules shared by every calculator. Each calculator’s specific formula is on its own page under “How it is calculated”, and every result includes a step-by-step breakdown.
Calculation in your browser
All arithmetic runs on your device in JavaScript. Your data is not sent to any server. Every formula is covered by automated tests with sample and edge cases.
Example values and prices
Prices (electricity, fuel, materials, labour…) vary by country, supplier and time, and there is no single, up-to-date, verifiable source for every market. That is why every price is configurable and starting values are examples to show how the tool works, not official prices or market averages.
Currencies
You can choose euro, US dollar or pound sterling independently of language. We never convert amounts with made-up exchange rates: when you switch currency, amounts stay as they are and you can optionally convert them by entering a manual rate.
Units
Everything is calculated internally in SI units. When you choose imperial, US customary units are used (US gallon, miles, feet, pounds) with these exact or standard equivalences:
| Quantity | Conversion |
|---|---|
| km ↔ mi | 1 mi = 1.609344 km |
| m ↔ ft | 1 ft = 0.3048 m |
| m² ↔ ft² | 1 ft² = 0.09290304 m² |
| L ↔ gal | 1 US gal = 3.785411784 L |
| kg ↔ lb | 1 lb = 0.45359237 kg |
| L/100 km ↔ mpg (US) | L/100 km = 235.215 ÷ mpg (US) |
| °C ↔ °F | °F = °C × 9/5 + 32 |
| m³ ↔ yd³ | 1 yd³ = 0.764554858 m³ |
Rounding
Intermediate calculations are not rounded; only displayed results are. Quantities bought in whole units (tins, boxes, bags, tiles) are always rounded up. Average months use 52 weeks ÷ 12 and years use 365 days.
Country rules
We don’t automatically apply any country’s taxes or regulations. Where a result depends on them (for example VAT or sales tax on a bill) it appears as a configurable field.
Limitations
Results are only as accurate as the data you enter and do not replace a bill, a professional quote, an engineering calculation or financial, tax or legal advice.
Last general review: 2026-11-10.