Whether you're following a recipe from another country, reading a foreign weather report, or shipping a package overseas, you'll eventually hit a unit you don't think in. The good news: most everyday conversions come down to a handful of fixed factors you can memorize or look up in seconds.
Length: inches, miles, and meters
Length is the most common conversion people need. The two anchors worth knowing:
- 1 inch = 2.54 cm (exactly)
- 1 mile ā 1.609 km
From those, everything else follows. A foot is 12 inches, so 1 foot = 30.48 cm. A meter is about 39.37 inches.
| From | To | Multiply by |
|---|---|---|
| inches | cm | 2.54 |
| cm | inches | 0.3937 |
| miles | km | 1.609 |
| km | miles | 0.6214 |
Example: a 6-foot person is 6 Ć 30.48 = 182.88 cm.
Weight: pounds and kilograms
For weight (technically mass), the key factor is:
- 1 kg ā 2.205 lb
- 1 lb ā 0.4536 kg
So a 70 kg adult weighs about 70 Ć 2.205 = 154.4 lb. Going the other way, a 10 lb bag of flour is roughly 4.54 kg.
Temperature: the one with a formula
Temperature is trickier because it doesn't scale from zero like length or weight ā you need a formula, not just a multiplier:
- Ā°F = (Ā°C Ć 9/5) + 32
- Ā°C = (Ā°F ā 32) Ć 5/9
A few reference points make it intuitive:
| Celsius | Fahrenheit | Meaning |
|---|---|---|
| 0 Ā°C | 32 Ā°F | Water freezes |
| 20 Ā°C | 68 Ā°F | Room temperature |
| 37 Ā°C | 98.6 Ā°F | Body temperature |
| 100 Ā°C | 212 Ā°F | Water boils |
For example, a 25 Ā°C day is (25 Ć 9/5) + 32 = 77 Ā°F ā pleasant and warm.
How to use it
Doing this math by hand works, but it's slow and error-prone when you're juggling decimals. The Unit Converter handles length, weight, and temperature instantly ā just type a value, pick your units, and read the result. No app to install, and it runs right in your browser.
If you're converting other kinds of numbers, useKits has matching tools nearby. The File Size Converter translates between bytes, KB, MB, and GB, while the Number Base Converter flips numbers between binary, decimal, and hexadecimal. Bookmark the set and you'll never reach for a calculator (or a search engine) for a conversion again.
A final tip: when accuracy matters ā like dosing medication or cutting materials ā always double-check with a tool rather than rounding in your head. The difference between 2.5 and 2.54 can add up fast across many units.