How to use the converter
Pick a category, type a value, choose the units, and the result appears as you type. ⇄ swaps the direction. The line underneath shows the one-unit rate in both directions so you can do the mental arithmetic next time.
Popular conversions
Each has its own page with a reference table and formula:
Formulas worth remembering
| Conversion | Multiply by |
|---|---|
| inches → cm | 2.54 |
| feet → meters | 0.3048 |
| miles → km | 1.609 |
| pounds → kg | 0.4536 |
| ounces → grams | 28.35 |
| US gallons → liters | 3.785 |
| US cups → mL | 236.6 |
| mph → km/h | 1.609 |
| acres → sq ft | 43,560 |
Temperature is the exception — it needs an offset, not just a multiplier: °F = °C × 1.8 + 32.
Metric vs US customary
The US is one of three countries that never adopted the metric system for everyday use, so cooking, body measurements, road distances and DIY all mix units depending on where a product or recipe came from. A few things that catch people out:
- Cups and spoons are volume, not weight. A cup of flour weighs about 125 g; a cup of sugar about 200 g. Recipes in grams are more reliable.
- Imperial ≠ US customary. The UK gallon (4.546 L) is 20% larger than the US gallon (3.785 L); the UK pint is 568 mL vs 473 mL. Both share the same inch, foot, pound and ounce.
- Stone (14 lb) is still common for body weight in the UK and Ireland.
- Kilobyte confusion. Storage makers use 1 KB = 1,000 bytes; operating systems often use 1 KiB = 1,024. That’s why a “1 TB” drive shows as 931 GB — both are in the Data category here.
- Nautical miles and knots are based on the Earth’s circumference (1 nm = 1,852 m), which is why aviation and shipping still use them.
Precision
Results show up to six significant figures, which is more than any tape measure or kitchen scale delivers. Conversion factors are the exact legal definitions where one exists (inch, pound, gallon) and standard reference values otherwise.
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54. The inch has been defined as 25.4 mm since 1959, so the conversion is exact — divide centimeters by 2.54 to get inches.
How many pounds is a kilogram?
2.20462 pounds. A pound is defined as exactly 0.45359237 kg, so kilograms × 2.2046 gives pounds. For a quick estimate, double it and add 10%.
What's the formula for Celsius to Fahrenheit?
°F = °C × 9/5 + 32. Going the other way, °C = (°F − 32) × 5/9. Quick check: 0 °C = 32 °F, 100 °C = 212 °F, and −40 is the same in both.
Are US and UK fluid ounces the same?
No. A US fluid ounce is 29.57 mL; a UK (imperial) fluid ounce is 28.41 mL, and a UK pint is 20 imperial ounces versus 16 US ounces in a US pint. This converter uses US units.
Last updated August 27, 2026.