Guides/Unit conversion

Metric and imperial unit conversion

Recipes, shipping labels, travel weather, and DIY projects often mix metric and US customary units. You do not need every factor memorized — convert through a base unit, or use a reliable converter.

Useful conversion factors

Length: 1 inch = 2.54 cm; 1 foot = 0.3048 m; 1 mile = 1.609344 km
Weight: 1 kg ≈ 2.20462 lb; 1 lb = 16 oz ≈ 453.592 g
Temperature: °F = °C × 9/5 + 32; °C = (°F − 32) × 5/9; K = °C + 273.15
Volume (US liquid): 1 US gallon ≈ 3.78541 L; 1 US fl oz ≈ 29.5735 mL

Note: UK imperial gallons differ from US gallons. OurUnit Converter uses US liquid volume units.

How conversion works

For length, weight, and volume, convert the value into a base unit (metres, kilograms, litres), then divide by the factor for the target unit. Temperature is special: use the formulas above instead of a simple multiply. Deep dive:Celsius to Fahrenheit explained.

Worked examples

Screen size: 15.6 in × 2.54 = 39.624 cm diagonal.
Luggage: 23 kg × 2.20462 ≈ 50.7 lb.
Weather: 25 °C → 25 × 1.8 + 32 = 77 °F.
Fuel/recipe: 2 US gallons × 3.78541 ≈ 7.57 L.
Height: 180 cm ÷ 2.54 ≈ 70.87 in ≈ 5 ft 10.9 in.
Package weight: 5 lb × 0.45359237 ≈ 2.27 kg.

Common mistakes

Mixing US and UK gallons (UK gallon is larger ≈ 4.546 L).
Treating temperature like length (you cannot “multiply °C by 2.54”).
Rounding too early in multi-step DIY cuts — keep more decimals until the final result.

When to use which tool

Unit Converter — length, weight, temp, volume in one place.
°C ↔ °F guide — weather and oven temperatures only.
Percentage Calculator — not for units; use for discounts and ratios.

Convert online

Use the freeUnit Converterfor length, weight, temperature, and volume. Instant results, private to your browser.