What This Unit Converter Covers
Six categories, all the everyday units:
| Category | Units |
|---|---|
| Length | mm, cm, m, km, inch, foot, yard, mile |
| Weight | mg, g, kg, tonne, ounce, pound, stone |
| Temperature | Celsius, Fahrenheit, Kelvin |
| Volume | ml, liter, tsp/tbsp, cup, pint, quart, gallon |
| Speed | km/h, mph, m/s, knots |
| Data | KB, MB, GB, TB (and their binary siblings) |
Pick a category, enter a value, choose from/to — the result appears instantly, with the swap button reversing direction in one tap. Working with flat shapes or solids instead of single measures? The Area Calculator and Volume Calculator cover those end to end.
The Conversions Worth Memorizing
| Anchor | Value |
|---|---|
| 1 inch | 2.54 cm (exact) |
| 1 foot | 30.48 cm |
| 1 mile | 1.609 km |
| 1 kg | 2.205 lb |
| 1 stone | 14 lb = 6.35 kg |
| 1 US gallon | 3.785 L |
| 1 cup (US) | ~237 ml |
| 100 km/h | 62.1 mph |
Everything else derives from anchors: yards are 3 feet, tonnes are 1,000 kg, and metric's whole design is that prefixes are just ×1000 steps.
Temperature: The Odd One Out
Temperature scales have offset zeros, so conversion needs more than a multiplier:
| Reference | °C | °F |
|---|---|---|
| Water freezes | 0 | 32 |
| Room temperature | ~21 | ~70 |
| Body temperature | 37 | 98.6 |
| Water boils | 100 | 212 |
| Scales agree | −40 | −40 |
Mental shortcut: °C ≈ (°F − 30) ÷ 2 — 70°F → about 20°C, close enough for weather.
Traps and Gotchas
- US vs imperial (UK) volumes differ: a UK gallon is 4.546 L vs the US 3.785 L; UK pints are bigger too. Recipes and fuel economy cross-contaminate badly here.
- Fluid ounces ≠ ounces: one measures volume, the other weight — "8 oz of flour" by weight is not one US cup.
- Data units are double-defined: marketing GB = 10⁹ bytes, OS GiB = 2³⁰ — the reason a "1 TB" drive shows ~931 "GB". This converter labels both conventions.
- Cups are regional: US ~237 ml, metric cup 250 ml, old imperial 284 ml — meaningful in baking.
- Nautical vs statute miles: knots are nautical miles/hour (1.852 km/h each), used in aviation and sailing.
The Bottom Line
Unit conversion is one exact multiplication — plus knowing which of the world's overlapping definitions you're holding. The converter above handles both parts; the anchor table and the gotchas list are what keep recipes, road trips, and hard-drive purchases from mysterious failure. For height/weight in health math, the BMI Calculator converts inline.