Length and distance conversions that actually hold up
Start with the one number worth memorizing: an inch is exactly 2.54 centimetres. Not approximately — exactly, by international agreement. That's the whole reason the CM to Inches Calculator and Inches to CM Calculator can give you a clean answer instead of a rounded guess.
Longer distances run on a different factor — 1.609344, baked into both the KM to Miles Calculator and the Miles to KM Calculator. Height trips people up more than either of these, honestly. Most people don't want "1.78 metres" — they want feet and inches. Run it through the Meters to Feet Calculator and split the leftover decimal into inches rather than rounding to the nearest foot; that rounding is where most height conversions quietly go wrong.
Temperature and pressure: the conversions with a catch
Here's the thing about temperature: you can't just multiply your way from one scale to the other. Celsius and Fahrenheit start at different zeros, so there's an offset involved as well as a ratio. That's why 0°C lands on 32°F instead of 0°F, and it's exactly what the Celsius to Fahrenheit Calculator and Fahrenheit to Celsius Calculator handle for you.
If you're doing anything with gas laws, forget Celsius and Fahrenheit — you want the Celsius to Kelvin Calculator, since Kelvin is the absolute scale science actually runs on.
Pressure has a similar split. Tyre pressures and equipment specs jump between bar and PSI depending on which side of the Atlantic (or which manufacturer) wrote the manual, and the Bar to PSI Calculator just settles the argument.
Weight and volume, or why your suitcase and your recipe both need this
Guessing at weight limits is expensive. Airlines and couriers each quote allowances in whatever unit suits them, so it's worth checking with the KG to LBS Calculator or LBS to KG Calculator before you're standing at the check-in desk arguing about 2 kilos. Volume is messier still, because the same word means different things in different countries — a US gallon is about 17% smaller than an imperial one, which the Liters to Gallons Calculator already assumes on the US side. Recipes cross borders too, and when they do, the mL to Cups Calculator and oz to mL Calculator keep your measurements from turning a cake into a brick.
Frequently asked questions
- How many centimetres are in an inch?
- 2.54, exactly. It's not a rounded measurement — it was fixed as an international definition back in 1959. Going backward, just divide your centimetre figure by 2.54.
- Is a US gallon the same as a UK gallon?
- No, and this trips people up constantly. A US gallon holds about 3.785 litres; an imperial gallon holds about 4.546 litres. The UK one is roughly a fifth bigger.
- What's a quick way to convert Celsius to Fahrenheit without a calculator?
- Double the Celsius number, then add 30. It's not exact — 20°C gives you 70°F as a rough estimate versus the real 68°F — but it's close enough for weather chat. If you need the real number, it's (°C × 9/5) + 32.
- Are fluid ounces and regular ounces the same thing?
- No. One measures volume, the other measures weight, and mixing them up ruins recipes. Water is the coincidence that confuses everyone — 8 fl oz of water happens to weigh close to 8 oz. Flour doesn't play along the same way; 8 fl oz of it weighs noticeably less than 8 oz.
- How many kilograms is 1 pound?
- 0.45359237 kg. Flip it around and a kilogram is about 2.2046 pounds. If you just need a ballpark in your head, halve the pound figure and shave off another tenth.