Quick Reference

Metric vs Imperial: The Complete Cheat Sheet

Metric and imperial units cover the same four everyday dimensions: length, weight, volume, and temperature. This cheat sheet gives you the key conversion factors, the mental shortcuts that work without a calculator, and the anchor points that are worth memorizing.

Length

The most-used length conversions: 1 inch = 2.54 cm. 1 foot = 30.48 cm. 1 meter = 3.281 feet = 39.37 inches. 1 kilometer = 0.6214 miles. 1 mile = 1.609 km.

Mental shortcuts: km × 0.6 ≈ miles (exact: 0.6214). Miles × 1.6 ≈ km (exact: 1.609). These work within 3% for any practical distance.

  • 1 in = 2.54 cm
  • 1 ft = 30.48 cm
  • 1 yd = 91.44 cm = 0.9144 m
  • 1 mile = 1.609 km
  • 1 km = 0.621 miles
  • 1 m = 3.281 ft = 39.37 in

Weight

1 pound = 0.4536 kg. 1 kilogram = 2.205 pounds. 1 ounce = 28.35 grams. 1 stone (UK) = 6.35 kg = 14 lbs.

Mental shortcut: lbs ÷ 2.2 ≈ kg. kg × 2.2 ≈ lbs. Accurate to within 0.2%.

  • 1 oz = 28.35 g
  • 1 lb = 453.6 g = 0.4536 kg
  • 1 stone = 6.35 kg
  • 1 kg = 2.205 lb
  • 1 tonne (metric) = 1,000 kg = 2,205 lb
  • 1 ton (US short) = 2,000 lb = 907.2 kg

Volume and Temperature

Volume: 1 US gallon = 3.785 liters. 1 liter = 0.264 US gallons. 1 US fluid ounce = 29.57 mL. 1 UK pint = 568 mL. 1 US cup = 237 mL.

Temperature: °F = (°C × 1.8) + 32. °C = (°F − 32) ÷ 1.8. Key anchors: 0°C = 32°F (freeze), 20°C = 68°F (room), 37°C = 98.6°F (body), 100°C = 212°F (boil).

  • 1 tsp = 4.93 mL
  • 1 tbsp = 14.79 mL
  • 1 US fl oz = 29.57 mL
  • 1 US cup = 237 mL
  • 1 US pint = 473 mL
  • 1 US quart = 0.946 L
  • 1 US gallon = 3.785 L

A Four-Step Mental Conversion Method

When you encounter an unfamiliar unit and need a quick estimate, follow these four steps.

Mental conversion method
1Identify the categoryIs this length, weight, volume, or temperature?2Recall the key factorkm × 0.6, lbs ÷ 2.2, gallons × 3.8, (°C × 1.8) + 323Apply the shortcutMultiply or divide — no calculator needed for estimates4Sanity-check the resultDoes it make physical sense? 100 km ≈ 60 miles ✓

Conclusion

Four categories, four mental shortcuts: km × 0.6 = miles, lbs ÷ 2.2 = kg, gallons × 3.8 = liters, (°C × 1.8) + 32 = °F. These cover 90% of everyday conversions without a calculator. The remaining 10% — cooking quantities, tire pressures, screen sizes — are better handled by a converter.

Frequently Asked Questions

Why does the US use imperial units instead of metric?

Historical adoption at the time of independence (1776), before metric was standardized, combined with failed metrication attempts in the 1970s. Cost and political resistance blocked the switch.

Which is easier — metric or imperial?

Metric is objectively simpler: all units relate by powers of 10. Imperial requires memorizing irregular conversion factors (12 inches in a foot, 3 feet in a yard, 5,280 feet in a mile, 16 ounces in a pound).

Which countries still use imperial?

The United States uses imperial for most everyday purposes. The UK uses a mix (miles for roads, pints for beer, but kg in supermarkets). Myanmar and Liberia have also not fully adopted metric.

How do I remember metric-to-imperial conversions?

Use four anchor shortcuts: km × 0.6 = miles, lbs ÷ 2.2 = kg, gallons × 3.8 = liters, and the temperature formula (°C × 1.8) + 32 = °F.

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