You don’t need to memorize a physics textbook — you need the dozen conversions that come up in kitchens, on road trips, and while reading a weather app abroad. Here they are, with the mental shortcuts that get you close enough for real life.
Short answer: 1 inch = 2.54 cm, 1 mile ≈ 1.6 km, 1 kg ≈ 2.2 lb, and °F ≈ (°C × 2) + 30 for a rough read. For anything you’re cooking or shipping, the Unit Converter gives the exact figure instantly.
Length and distance
| From | To | Multiply by |
|---|---|---|
| Inches | Centimeters | 2.54 |
| Feet | Meters | 0.305 |
| Miles | Kilometers | 1.61 |
| Meters | Feet | 3.28 |
Mental trick: for miles → km, add half again plus a little (10 mi → 16 km). The Fibonacci sequence is uncannily good here — 5, 8, 13, 21 in miles are almost exactly 8, 13, 21, 34 in km.
Weight
| From | To | Multiply by |
|---|---|---|
| Pounds | Kilograms | 0.454 |
| Kilograms | Pounds | 2.20 |
| Ounces | Grams | 28.35 |
| Stone | Pounds | 14 |
Mental trick: to go kg → lb, double it and add 10% (70 kg → 140 + 14 = 154 lb). Body-weight math like this feeds straight into a Calorie Calculator, which usually wants kilograms even if you think in pounds.
Temperature
The one worth memorizing because you can’t fake it:
- Exact: °F = (°C × 9/5) + 32
- Rough: double the Celsius and add 30 — fine for “do I need a jacket”
- Anchors: 0°C = 32°F (freezing), 37°C = 98.6°F (body), 100°C = 212°F (boiling)
The kitchen (where mistakes are expensive)
Cooking is where conversions bite, because a US cup, a UK cup, and a “metric cup” are all different, and a US pint ≠ a UK pint.
| Measure | Metric |
|---|---|
| 1 US cup | 240 mL |
| 1 tablespoon (US) | 15 mL |
| 1 teaspoon | 5 mL |
| 1 US pint | 473 mL |
| 1 UK pint | 568 mL |
| 350°F oven | 177°C |
When you’re scaling a recipe up for a crowd — doubling, tripling, or working out “60% of this batch” — the Percentage Calculator keeps the ratios honest so nothing comes out under-seasoned.
Why “close enough” is usually fine — until it isn’t
For deciding what to wear or how far a drive is, the mental tricks above are plenty. The moment precision matters — a baking recipe, a medication dose, a package that has to fit a shipping limit — round-off errors stack up fast. That’s the line: estimate for comfort, convert exactly for consequences. The Unit Converter covers length, weight, volume, temperature, and more, so you’re not juggling four different formulas in your head at once.