Unit Conversions Guide: Length, Weight, Volume & Temperature
Last updated: December 2024 • 9 min read
Whether you're cooking with a recipe from another country, traveling abroad, or working on an international project, converting between units is an essential skill. This comprehensive guide covers the most common conversions you'll need, with simple formulas and quick reference tables.
Length Conversions
Metric System
The metric system is based on powers of 10:
- 1 kilometer (km) = 1,000 meters
- 1 meter (m) = 100 centimeters
- 1 centimeter (cm) = 10 millimeters
Metric ↔ Imperial
| From | To | Multiply by |
|---|---|---|
| Inches | Centimeters | 2.54 |
| Centimeters | Inches | 0.3937 |
| Feet | Meters | 0.3048 |
| Meters | Feet | 3.281 |
| Miles | Kilometers | 1.609 |
| Kilometers | Miles | 0.6214 |
Quick Tip: To roughly convert km to miles, multiply by 0.6 (or divide by 1.6).
100 km ≈ 62 miles
Weight/Mass Conversions
| From | To | Multiply by |
|---|---|---|
| Ounces (oz) | Grams (g) | 28.35 |
| Grams | Ounces | 0.03527 |
| Pounds (lb) | Kilograms (kg) | 0.4536 |
| Kilograms | Pounds | 2.205 |
| Stone | Kilograms | 6.35 |
Quick Tip: To convert kg to pounds, multiply by 2.2.
70 kg ≈ 154 lbs
Volume Conversions
| From | To | Multiply by |
|---|---|---|
| US Cups | Milliliters | 236.6 |
| US Fluid Ounces | Milliliters | 29.57 |
| Liters | US Gallons | 0.2642 |
| US Gallons | Liters | 3.785 |
| UK Pints | Liters | 0.5683 |
Cooking Quick Reference:
- 1 cup ≈ 240 ml
- 1 tablespoon ≈ 15 ml
- 1 teaspoon ≈ 5 ml
Temperature Conversions
°F to °C: (°F - 32) × 5/9
°C to °F: (°C × 9/5) + 32
°C to Kelvin: °C + 273.15
Common Temperature Reference Points
| Description | Celsius | Fahrenheit |
|---|---|---|
| Water freezes | 0°C | 32°F |
| Room temperature | 20-22°C | 68-72°F |
| Body temperature | 37°C | 98.6°F |
| Water boils | 100°C | 212°F |
| Oven (moderate) | 180°C | 350°F |
Quick Tip: For a rough °C to °F conversion, double the Celsius and add 30.
20°C: 20 × 2 + 30 = 70°F (actual: 68°F) — close enough!
Area Conversions
| From | To | Multiply by |
|---|---|---|
| Square feet | Square meters | 0.0929 |
| Square meters | Square feet | 10.764 |
| Acres | Hectares | 0.4047 |
| Hectares | Acres | 2.471 |
Speed Conversions
mph to km/h: mph × 1.609
km/h to mph: km/h × 0.6214
Quick Reference:
- 30 mph ≈ 48 km/h
- 60 mph ≈ 97 km/h
- 100 km/h ≈ 62 mph
Calculate Conversions
Use our calculator for quick unit conversions and calculations.
Try Calculator →Length Conversion Reference Table
The metric and imperial systems are used side by side in many countries. Here are the key length conversion factors you'll need most often:
| Unit | mm | cm | m | km | inch | foot | mile |
|---|---|---|---|---|---|---|---|
| 1 mm | 1 | 0.1 | 0.001 | 0.000001 | 0.0394 | 0.00328 | — |
| 1 cm | 10 | 1 | 0.01 | 0.00001 | 0.394 | 0.0328 | — |
| 1 m | 1,000 | 100 | 1 | 0.001 | 39.37 | 3.281 | 0.000621 |
| 1 km | 1,000,000 | 100,000 | 1,000 | 1 | 39,370 | 3,281 | 0.6214 |
| 1 inch | 25.4 | 2.54 | 0.0254 | — | 1 | 0.0833 | — |
| 1 foot | 304.8 | 30.48 | 0.3048 | 0.000305 | 12 | 1 | 0.000189 |
| 1 mile | 1,609,344 | 160,934 | 1,609.3 | 1.6093 | 63,360 | 5,280 | 1 |
Temperature Conversions: Celsius, Fahrenheit, and Kelvin
Temperature conversion is one of the most commonly needed conversions when travelling or cooking. The formulas:
- °C to °F: (°C × 9/5) + 32
- °F to °C: (°F − 32) × 5/9
- °C to K: °C + 273.15
| Reference Point | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Cold winter day | −10 | 14 | 263.15 |
| Room temperature | 20 | 68 | 293.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Hot summer day | 35 | 95 | 308.15 |
| Water boils | 100 | 212 | 373.15 |
Cooking Conversions: A Kitchen Reference
Recipe conversions are one of the most practical everyday uses of unit conversion. Here's a complete kitchen reference:
| Measurement | Teaspoons | Tablespoons | Cups (US) | ml |
|---|---|---|---|---|
| 1 teaspoon | 1 | ⅓ | 1/48 | 4.93 |
| 1 tablespoon | 3 | 1 | 1/16 | 14.79 |
| ¼ cup | 12 | 4 | ¼ | 59 |
| ½ cup | 24 | 8 | ½ | 118 |
| 1 cup | 48 | 16 | 1 | 237 |
| 1 pint (US) | 96 | 32 | 2 | 473 |
Frequently Asked Questions
Why do different countries use different unit systems?
The metric system was developed in France during the 18th century for scientific consistency. Most countries adopted it, but the US, UK (partially), and a few others retained traditional systems for historical and practical reasons.
Is a UK pint the same as a US pint?
No! A UK pint is 568 ml, while a US pint is only 473 ml. The UK pint is about 20% larger.
What's the easiest way to remember conversions?
Focus on rough approximations first: 1 inch ≈ 2.5 cm, 1 kg ≈ 2.2 lbs, 1 mile ≈ 1.6 km. These round numbers are easier to use mentally.
Alex van den Berg
Financial Educator & Mathematics Writer
Alex has 8+ years of experience in personal finance education and mathematics instruction. He writes practical guides on financial calculations, everyday maths, and how to use digital tools to make smarter money decisions.