Metric vs. Imperial: The Complete Unit Conversion Cheatsheet

Two systems of measurement coexist in the world: the metric system (used by most countries) and the imperial system (used primarily in the United States, with some overlap in the UK and Canada). Switching between them is a daily reality for anyone who travels, cooks internationally, works in engineering, or follows foreign sports.

This guide covers every common conversion with exact formulas and practical mental shortcuts.

Length

Metric	Imperial	Exact conversion
1 km	0.6214 miles	× 0.6214
1 m	3.281 feet	× 3.281
1 m	39.37 inches	× 39.37
1 cm	0.3937 inches	× 0.3937
1 mm	0.03937 inches	× 0.03937

Quick mental shortcuts: - km → miles: multiply by 0.6 (or, more precisely, multiply by 6, divide by 10) - miles → km: multiply by 1.6 - cm → inches: divide by 2.54 - feet → cm: multiply by 30.48 (roughly: × 30) - Rough check: 5 km ≈ 3.1 miles; 100 m ≈ 109 yards

Body height conversions (common reference)

cm	ft/in
150	4'11"
160	5'3"
170	5'7"
180	5'11"
190	6'3"

Weight (Mass)

Metric	Imperial	Exact conversion
1 kg	2.205 lbs	× 2.205
1 g	0.03527 oz	× 0.03527
1 metric ton (tonne)	2,205 lbs	× 2205

Quick mental shortcuts: - kg → lbs: multiply by 2.2 (close enough for most uses) - lbs → kg: divide by 2.2 (or multiply by 0.453) - stone (UK): 1 stone = 14 lbs = 6.35 kg

Temperature

Temperature is the most counterintuitive conversion because it's not a simple multiplication — it involves an offset:

Formula	Direction
°C = (°F − 32) × 5/9	Fahrenheit → Celsius
°F = (°C × 9/5) + 32	Celsius → Fahrenheit
K = °C + 273.15	Celsius → Kelvin

Key reference points: | °C | °F | Meaning | |----|-----|---------| | −40 | −40 | Same value in both scales | | 0 | 32 | Water freezes | | 20 | 68 | Comfortable room temperature | | 37 | 98.6 | Human body temperature | | 100 | 212 | Water boils |

Mental shortcut for everyday temperatures: - °C → °F: Double it, then add 30 (approximate, works from −10°C to 40°C) - °F → °C: Subtract 30, then halve

Volume

Liquid volume

Metric	US Imperial	Exact
1 L	2.113 US pints	× 2.113
1 L	1.057 US quarts	× 1.057
1 L	0.264 US gallons	× 0.264
1 mL	0.0338 fl oz	× 0.0338
1 mL	0.2029 US tsp	× 0.2029

Cooking measures

US	Metric
1 teaspoon (tsp)	4.93 mL
1 tablespoon (tbsp)	14.79 mL
1 fl oz	29.57 mL
1 cup	236.6 mL
1 pint	473.2 mL
1 quart	946.4 mL
1 gallon	3.785 L

Note: UK and US volumes differ. A UK pint is 568 mL, a US pint is 473 mL.

Area

Metric	Imperial	Exact conversion
1 km²	0.3861 sq miles	× 0.3861
1 hectare (ha)	2.471 acres	× 2.471
1 m²	10.76 sq ft	× 10.76
1 cm²	0.155 sq in	× 0.155

Quick check: 1 football field ≈ 0.72 acres ≈ 0.29 ha

Speed

km/h	mph	Notes
50	31	Typical urban speed limit
80	50	Rural road
100	62	Motorway
120	75	Highway speed

Formula: mph = km/h × 0.6214 (or roughly: divide by 1.6)

Pressure

Metric	Imperial/Other	Exact
1 bar	14.50 psi	× 14.50
1 kPa	0.1450 psi	× 0.1450
1 atm	14.696 psi	= 101,325 Pa

Tyre pressure is often given in psi in the US and bar or kPa elsewhere. A typical car tyre runs at about 32–35 psi = 2.2–2.4 bar.

Why Two Systems Still Coexist

The metric system was formally adopted in France in 1795 and has since spread to every country except the United States, Liberia, and Myanmar (for official use). Even the US uses metric internally for science, medicine, and military applications.

The persistence of imperial units in everyday American life — miles on road signs, pounds on grocery labels, Fahrenheit in weather forecasts — is largely a matter of cultural inertia. Changing infrastructure, habits, and education simultaneously is expensive and slow.

Practically, anyone who operates internationally needs to be comfortable with both systems.

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