Conversion calculators

Why unit conversions cause more trouble than they should

The UK has been officially metric for the best part of fifty years and yet, on any given day, you can be asked your height in feet and inches, your weight in stones, the distance to the next service station in miles, the petrol you're filling up in litres, and the room temperature in Celsius. The cookbook on the shelf might be metric, but the recipe your grandmother wrote out is in cups. Your imported car has a manual in km/L. None of it is going to change soon, and none of it makes mental arithmetic easy.

The other complication is that some "imperial" units are not the same on both sides of the Atlantic. A US gallon is not a UK gallon. A US tablespoon is not a UK tablespoon. Cup measures vary depending on whose cookbook you're reading. A converter that doesn't tell you which cup it's using is, in baking terms, the difference between a sponge that rises and a sponge that doesn't. The Cooking Measurements Converter separates UK, US and metric on purpose, because the alternative is a ruined batch of biscuits.

Where the input number really comes from

Most conversions start with a number someone else gave you: a recipe, a spec sheet, a dosage, a customs form, a sat-nav. The first job is reading what unit it's actually in. American recipes assume US cups even when they don't say so. European car spec sheets quote fuel economy in litres per 100 kilometres, which is the inverse of miles per gallon, so a smaller number is better. Aviation altitudes are in feet, even in countries that are otherwise fully metric. Knowing which convention applies to the source is more than half the battle.

For everyday measurements, a tape measure or kitchen scale gives you the cleanest input. For things you're estimating, like a room size or a parcel weight, round to a sensible precision before converting. Carrying six decimal places of "approximately a metre and a half" is fake precision, and it tends to look worse, not better, in the converted answer.

Common mistakes worth avoiding

The first is mixing dry and liquid measurements. A cup of flour weighs nothing like a cup of water, and converting "1 cup flour" to grams via a generic volume formula gives you nonsense. Use a converter that knows about ingredient density, or weigh the ingredient instead.

The second is forgetting that temperature conversions are not multiplications. Celsius and Fahrenheit don't share a zero. You can't scale them, you have to translate them. The same goes for time zones, where daylight saving moves the goalposts twice a year.

The third is precision laundering. If your input is "about three feet", your output is "about a metre". It is not "0.9144 metres". The Unit Converter will give you that level of precision because the maths supports it, but pasting the long decimal into a quote or a contract is how you end up arguing with a contractor about two millimetres that nobody actually measured.

How to pick the right tool

For everyday units, the unit converter handles length, mass, volume, temperature, speed and area in one place. For recipes, use the cooking converter so you get the right cup. For schedules across borders, the Time Zone Converter handles DST without the usual hour-out mistakes. For developer-specific work, the number base and Roman numeral tools cover the niches the everyday converter shouldn't try to. Pick by question, not by tool name, and you'll usually land in the right place.

Why yet another unit converter

Most converters on the internet make you pick the "to" unit before they'll show you anything. That's fine if you already know which one you want. But half the time you're converting because you're not sure, and you want to see "6 foot 2 in stones" and "6 foot 2 in metres" side by side without clicking twice. This one gives you every unit at once.

It also runs in the browser. Nothing uploaded, no account, no ads shoved between the input and the result.