My official tables for converting imperial/US customary units to metric in my head.
Tip: Practice makes perfect. Don't try memorizing all these in one go!
| Imperial Unit | Exact Value | Approximation | Steps to Convert |
|---|---|---|---|
| Inch | 2.54 cm | ≈ 2.5 cm | Multiply by 10, halve twice |
| Foot | 0.3048 m | ≈ 0.3 m | Multiply by 3, divide by 10 |
| Yard | 0.9144 m | ≈ 0.9 m | Subtract 10% |
| Mile | 1.609344 km | ≈ 1.6 km | Double 4 times, divide by 10 |
| Imperial Unit | Exact Value | Approximation | Steps to Convert |
|---|---|---|---|
| Square Inch | 6.4516 cm² | ≈ 6.25 cm² | Multiply by 100, halve 4 times |
| Square Foot | 0.09290304 m² | ≈ 0.09 m² | Divide by 10, subtract 10% |
| Acre | 0.40468564224 ha | ≈ 0.4 ha | Double twice, divide by 10 |
| Square Mile | 2.589988110336 km² | ≈ 2.5 km² | Multiply by 10, halve twice |
| Imperial Unit | Exact Value | Approximation | Steps to Convert |
|---|---|---|---|
| US Teaspoon | 4.92892 ml | ≈ 5 ml | Multiply by 10, halve |
| US Fluid Ounce | 29.5735295625 ml | ≈ 30 ml | Multiply by 3, then 10 |
| US Cup | 0.2365882365 l | ≈ 0.25 l | Halve twice |
| US Gallon | 3.785411784 l | ≈ 4 l | Double twice |
| Imperial Unit | Exact Value | Approximation | Steps to Convert |
|---|---|---|---|
| Ounce | 28.349523125 g | ≈ 30 g | Multiply by 10, then 3 |
| Pound | 0.45359237 kg | ≈ 0.45 kg | Halve, subtract 10% |
| Stone | 6.35029318 kg | ≈ 6 kg | Double, then multiply by 3 |
| US Ton | 0.90718474 t | ≈ 0.9 t | Subtract 10% |
| Imperial Unit | Exact Value | Approximation | Steps to Convert |
|---|---|---|---|
| Miles/Hour | 0.44704 m/s | ≈ 0.45 m/s | Halve, subtract 10% |
| Pounds/Square Inch | 68.94757293 mbar | ≈ 70 mbar | Multiply by 7 (sorry), then 10 |
| Miles/Gallon | 0.425143707 km/l | ≈ 0.4 km/l | Double twice, divide by 10 |
| Fahrenheit | °C * 1.8 + 32 | ≈ (°F - 30) / 2 | Subtract 30, halve |