Exact metric conversions
12 conversions. All are exact. The inch, foot, yard, mile and pound have been defined in metric units since 1959; the others follow from them, so the long decimals are exact, not rounded. NIST gives the temperature rules as exact.
When a recipe, a science lab or a trip abroad switches between inches and centimeters or pounds and kilograms, these are the numbers behind every conversion chart. Most of them grow out of just two: the inch (2.54 cm) and the pound (0.45359237 kg).
Learn the two roots first, the inch and the pound, and derive the rest: a foot is 12 inches, so 12 x 2.54 = 30.48 cm. Working it out once is a strong encoding step, and it turns ten facts into two facts plus reasoning. Then use rounded versions for everyday sense (a mile is about 1.6 km, a kilogram about 2.2 pounds) and the exact ones when it matters. Chunk as length, weight, volume, temperature.
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Exact metric conversions
| Start with | equals | in | Exact? |
|---|---|---|---|
| 1 inch | 2.54 | centimeters | Exact by definition |
| 1 foot | 0.3048 | meters | Exact (12 x 2.54 cm) |
| 1 yard | 0.9144 | meters | Exact (36 x 2.54 cm) |
| 1 mile | 1.609344 | kilometers | Exact (5,280 x 0.3048 m) |
| 1 nautical mile | 1,852 | meters | Exact by definition |
| 1 pound | 0.45359237 | kilograms | Exact by definition |
| 1 ounce (weight) | 28.349523125 | grams | Exact (1/16 pound) |
| 1 U.S. gallon | 3.785411784 | liters | Exact (231 cubic inches) |
| 1 U.S. fluid ounce | 29.5735295625 | milliliters | Exact (1/128 gallon) |
| 1 liter | 1,000 | cubic centimeters | Exact by definition |
| °F to °C | subtract 32, then divide by 1.8 | degrees Celsius | Exact |
| °C to K | add 273.15 | kelvins | Exact |
Learn the two roots first, the inch and the pound, and derive the rest: a foot is 12 inches, so 12 x 2.54 = 30.48 cm. Working it out once is a strong encoding step, and it turns ten facts into two facts plus reasoning. Then use rounded versions for everyday sense (a mile is about 1.6 km, a kilogram about 2.2 pounds) and the exact ones when it matters. Chunk as length, weight, volume, temperature. · teddyrookbook.com/memory/challenges/metric-conversions/
Sources
- NIST Handbook 44 (2024), Appendix C: General Tables of Units of Measurement
- NIST: Approximate Conversions from U.S. Customary Measures to Metric (temperature: exact)
Checked October 30, 2026. Progress is kept on this device only (per learner). More lists: all memory challenges · memory games.