Everyday calculators and unit conversions: inches to centimetres, temperature, fuel consumption, electricity cost, tiles and paint, date differences, age and tips. This is the largest section on the site — 26 calculators, all of which compute immediately and none of which need an account.
Unit conversions are exact by definition rather than by estimate. An inch is exactly 25.4 millimetres under the 1959 international agreement, which is what the page cites. That is why this figure does not need re-checking every year — no government department can change it.
The building calculators — tiles, paint, concrete, firewood — work out quantities of material from the dimensions you enter. They know nothing about your particular shop or pack size, so the result is a quantity, not a shopping list.
Two things: unit conversions built on the factors in the BIPM SI Brochure, and practical sums — fuel, electricity, paint, tile, concrete, firewood, tyres, dates and age. What they share is that the answer is wanted immediately and without signing up.
Because the factors are not round. An inch is exactly 2.54 centimetres, a mile 1.609344 kilometres, a pound 0.45359237 kilograms — definitions taken from the BIPM SI Brochure and exact. Rounding intermediate steps accumulates error, so we round only at the end.
They are estimates from area and standard usage, and always need a margin on top: ten percent for paint and tile, five for concrete, since the base is rarely perfectly level. Running short costs more than having some left over, because batches differ in shade.
Yes. They walk the real Gregorian calendar with every leap year, rather than assuming a 365-day year and a thirty-day month. That simplification is exactly why other calculators come out a few days wrong over long spans.
Page updated 20/08/2026