Whether you’re cooking a foreign recipe, planning a road trip, shipping a package, or working on a DIY project, converting between measurement units is something everyone faces. Metric and imperial systems coexist in daily life — and switching between them shouldn’t require a math degree.
This guide covers the most common conversions for length, mass, and temperature, with quick reference tables you can bookmark and come back to.
Length Conversion
Length is the most frequently converted measurement. From measuring furniture to calculating travel distances, here’s everything you need.
Metric to Imperial
| Metric | Imperial | How to Convert |
|---|---|---|
| 1 mm | 0.039 inches | mm × 0.039 = inches |
| 1 cm | 0.394 inches | cm × 0.394 = inches |
| 1 m | 3.281 feet | m × 3.281 = feet |
| 1 m | 1.094 yards | m × 1.094 = yards |
| 1 km | 0.621 miles | km × 0.621 = miles |
Imperial to Metric
| Imperial | Metric | How to Convert |
|---|---|---|
| 1 inch | 2.54 cm | inches × 2.54 = cm |
| 1 foot | 0.305 m | feet × 0.305 = m |
| 1 yard | 0.914 m | yards × 0.914 = m |
| 1 mile | 1.609 km | miles × 1.609 = km |
Quick Mental Shortcuts
- Inches to cm: Multiply by 2.5 (close enough for most purposes). 8 inches ≈ 20 cm (exact: 20.32 cm)
- Feet to meters: Divide by 3. 12 feet ≈ 4 m (exact: 3.66 m)
- Miles to km: Multiply by 1.6. 60 mph ≈ 96 km/h (exact: 96.56 km/h)
- Km to miles: Multiply by 0.6. 100 km ≈ 60 miles (exact: 62.1 miles)
Real-World Examples
| Item | Metric | Imperial |
|---|---|---|
| Credit card width | 8.56 cm | 3.37 inches |
| Standard door height | 2.03 m | 6 feet 8 inches |
| Football field length | 109.7 m | 120 yards |
| Marathon distance | 42.195 km | 26.219 miles |
| Average human height | 1.75 m | 5 feet 9 inches |
Use our Length Converter to convert between 12+ units instantly — mm, cm, m, km, inches, feet, yards, miles, and more.
Mass Conversion
Mass (commonly called weight) conversions are essential for cooking, shipping, fitness, and international trade.
Metric to Imperial
| Metric | Imperial | How to Convert |
|---|---|---|
| 1 g | 0.035 ounces | g × 0.035 = oz |
| 1 kg | 2.205 pounds | kg × 2.205 = lbs |
| 1 tonne | 1.102 US tons | tonnes × 1.102 = US tons |
Imperial to Metric
| Imperial | Metric | How to Convert |
|---|---|---|
| 1 ounce | 28.35 g | oz × 28.35 = g |
| 1 pound | 0.454 kg | lbs × 0.454 = kg |
| 1 US ton | 0.907 tonnes | US tons × 0.907 = tonnes |
Quick Mental Shortcuts
- Kg to pounds: Double it and add 10%. 70 kg → 140 + 14 = 154 lbs (exact: 154.3 lbs)
- Pounds to kg: Halve it and subtract 10%. 154 lbs → 77 - 7.7 = 69.3 kg (exact: 69.9 kg)
- Grams to ounces: Divide by 28 (rough). 250 g ≈ 8.9 oz (exact: 8.82 oz)
Real-World Examples
| Item | Metric | Imperial |
|---|---|---|
| Standard apple | 150 g | 5.3 oz |
| Sack of rice | 5 kg | 11 lbs |
| Average adult weight | 70 kg | 154 lbs |
| Car | 1,500 kg | 3,307 lbs |
| Shipping container max | 30 tonnes | 33 US tons |
Temperature Conversion
Temperature conversions trip people up because the formulas are less intuitive than length or mass.
The Formulas
°C to °F: (°C × 9/5) + 32 = °F
°F to °C: (°F - 32) × 5/9 = °C
°C to K: °C + 273.15 = K
K to °C: K - 273.15 = °C
Common Temperature Reference
| Scenario | °C | °F | K |
|---|---|---|---|
| Absolute zero | -273.15 | -459.67 | 0 |
| Freezing point of water | 0 | 32 | 273.15 |
| Cold winter day | 0 | 32 | 273.15 |
| Cool room temperature | 15 | 59 | 288.15 |
| Room temperature | 22 | 71.6 | 295.15 |
| Warm summer day | 30 | 86 | 303.15 |
| Hot day | 35 | 95 | 308.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Boiling point of water | 100 | 212 | 373.15 |
| Baking temperature | 180 | 356 | 453.15 |
Quick Mental Shortcuts
- °C to °F: Double it and add 30. 30°C → 60 + 30 = 90°F (exact: 86°F)
- °F to °C: Subtract 30 and halve it. 90°F → 60 ÷ 2 = 30°C (exact: 32.2°C)
- These shortcuts are accurate enough for weather, not for cooking or science.
Oven Temperature Conversions
Recipes from different countries use different temperature scales. Here’s a quick cooking reference:
| Description | °C | °F | Gas Mark |
|---|---|---|---|
| Very low | 120 | 250 | ½ |
| Low | 150 | 300 | 2 |
| Moderate | 180 | 350 | 4 |
| Medium-hot | 200 | 400 | 6 |
| Hot | 220 | 425 | 7 |
| Very hot | 240 | 475 | 9 |
Conversion Cheat Sheet (Quick Reference)
Most-Used Conversions
| You Have | Multiply By | To Get |
|---|---|---|
| Inches | 2.54 | Centimeters |
| Feet | 0.305 | Meters |
| Miles | 1.609 | Kilometers |
| Kilometers | 0.621 | Miles |
| Pounds | 0.454 | Kilograms |
| Kilograms | 2.205 | Pounds |
| Ounces | 28.35 | Grams |
| °C | × 9/5 + 32 | °F |
| °F | - 32 × 5/9 | °C |
Kitchen Conversions
| Ingredient | Volume | Weight |
|---|---|---|
| 1 cup all-purpose flour | 240 ml | 120 g |
| 1 cup granulated sugar | 240 ml | 200 g |
| 1 cup butter | 240 ml | 227 g |
| 1 tablespoon | 15 ml | varies |
| 1 teaspoon | 5 ml | varies |
Why Accurate Conversion Matters
Small conversion errors can compound into big problems:
- Baking: A 10% error in flour (using 110g instead of 120g) can ruin a cake’s texture
- Shipping: Miscalculating package dimensions by 2 inches can double shipping costs
- Travel: Confusing miles and kilometers can lead to running out of fuel
- Medicine: A temperature conversion error can mean the difference between a normal reading and a fever
- Construction: A 0.5 cm error over 10 meters becomes a 5 cm gap at the end
When precision matters, use a conversion tool rather than mental math.
FAQ
How do I convert inches to cm? Multiply inches by 2.54. For example, 6 inches × 2.54 = 15.24 cm.
What’s the easiest way to convert Fahrenheit to Celsius? Subtract 30, then divide by 2. For weather temperatures, this shortcut is accurate enough. For exact conversion, use (°F - 32) × 5/9.
How many meters in a foot? One foot equals 0.3048 meters. For quick estimates, divide feet by 3.
What’s the difference between metric tonnes and US tons? A metric tonne = 1,000 kg. A US (short) ton = 907 kg. A UK (long) ton = 1,016 kg. The difference matters in shipping and trade.
How do I convert kg to pounds without a calculator? Double the kg value and add 10%. For 50 kg: 100 + 5 = 110 lbs (exact: 110.2 lbs).
Is 1 inch exactly 2.54 cm? Yes. Since 1959, the inch has been internationally defined as exactly 2.54 cm.
What’s the fastest way to convert between metric and imperial? Use a conversion tool. FreeToolz’s converters handle length, mass, temperature, speed, volume, area, and more — all instant, all free, no signup needed.
Convert any measurement instantly with FreeToolz’s free Length Converter — plus mass converter, temperature converter, and 10+ other unit tools. No signup required.