How to Use an Online Unit Converter
A modern online unit converter like the ToolMasta unit converter is straightforward to use:
- Select the category — choose from Length, Weight, Temperature, Volume, Area, Speed, etc.
- Enter your value — type the number you want to convert in the input field
- Select your source unit — pick the unit you are converting from (e.g. miles)
- Select your target unit — pick the unit you want to convert to (e.g. kilometres)
- Read the result — the converter calculates and displays the converted value instantly
Most converters update in real time as you type — there is no need to click a "convert" button. If you need to convert between many different units of the same quantity at once, look for a "show all" mode that displays the input value converted to every available unit simultaneously.
Length Conversions
Length is the most commonly converted quantity, driven by everything from buying imported products to running distances to reading scientific papers.
| From | To | Multiply by | Quick Example |
|---|---|---|---|
| Miles (mi) | Kilometres (km) | 1.60934 | 10 mi = 16.09 km |
| Kilometres (km) | Miles (mi) | 0.62137 | 5 km = 3.11 mi |
| Feet (ft) | Metres (m) | 0.3048 | 6 ft = 1.83 m |
| Metres (m) | Feet (ft) | 3.28084 | 1.8 m = 5.91 ft |
| Inches (in) | Centimetres (cm) | 2.54 | 12 in = 30.48 cm |
| Centimetres (cm) | Inches (in) | 0.3937 | 30 cm = 11.81 in |
Weight and Mass Conversions
Weight conversions matter most in cooking (recipes from the US use cups and ounces), gym and fitness (weight plates in kg vs lb), and online shopping (shipping weight limits).
| From | To | Multiply by | Quick Example |
|---|---|---|---|
| Pounds (lb) | Kilograms (kg) | 0.45359 | 150 lb = 68.04 kg |
| Kilograms (kg) | Pounds (lb) | 2.20462 | 70 kg = 154.3 lb |
| Ounces (oz) | Grams (g) | 28.3495 | 8 oz = 226.8 g |
| Grams (g) | Ounces (oz) | 0.03527 | 500 g = 17.64 oz |
| Stone (st) | Kilograms (kg) | 6.35029 | 11 st = 69.85 kg |
| Tonnes (t) | Pounds (lb) | 2204.62 | 1 t = 2,204.6 lb |
Temperature Conversions
Temperature conversions cannot use a simple multiplier because the zero points of the three main scales differ. Each requires both multiplication and addition or subtraction.
| Conversion | Formula | Example |
|---|---|---|
| °C to °F | °F = (°C × 9/5) + 32 | 20°C = 68°F |
| °F to °C | °C = (°F − 32) × 5/9 | 98.6°F = 37°C |
| °C to K | K = °C + 273.15 | 100°C = 373.15 K |
| K to °C | °C = K − 273.15 | 300 K = 26.85°C |
Volume Conversions
Volume conversions are most critical in cooking and in countries that mix metric and imperial systems. Note that US and UK definitions of gallons, pints, and fluid ounces differ significantly.
| From | To | Multiply by | Quick Example |
|---|---|---|---|
| US Cups | Millilitres (mL) | 236.588 | 1 cup = 236.6 mL |
| Millilitres (mL) | US Cups | 0.00423 | 250 mL = 1.06 cups |
| US Gallons | Litres (L) | 3.78541 | 1 gal = 3.79 L |
| Litres (L) | US Gallons | 0.26417 | 10 L = 2.64 gal |
| US fl oz | Millilitres (mL) | 29.5735 | 12 fl oz = 354.9 mL |
| UK Pints | Millilitres (mL) | 568.261 | 1 pint = 568.3 mL |
Area Conversions
Area conversions are essential for real estate (floor plans in m² vs sq ft), gardening (plots in acres vs hectares), and geographic data.
| From | To | Multiply by | Quick Example |
|---|---|---|---|
| Square feet (sq ft) | Square metres (m²) | 0.0929 | 500 sq ft = 46.5 m² |
| Square metres (m²) | Square feet (sq ft) | 10.7639 | 100 m² = 1,076 sq ft |
| Acres | Hectares (ha) | 0.4047 | 5 acres = 2.02 ha |
| Hectares (ha) | Acres | 2.4711 | 2 ha = 4.94 acres |
| Square miles | Square km | 2.58999 | 10 sq mi = 25.9 km² |
Speed Conversions
Speed conversions matter most for driving (speed limit signs when crossing borders), aviation (knots to km/h), and athletics (pace in min/km vs min/mile).
| From | To | Multiply by | Quick Example |
|---|---|---|---|
| mph | km/h | 1.60934 | 60 mph = 96.6 km/h |
| km/h | mph | 0.62137 | 100 km/h = 62.1 mph |
| m/s | km/h | 3.6 | 10 m/s = 36 km/h |
| Knots | km/h | 1.852 | 500 knots = 926 km/h |
| Knots | mph | 1.15078 | 500 knots = 575.4 mph |
The 20 Most-Searched Conversions (Quick Reference)
| # | Conversion | Formula / Factor | Example |
|---|---|---|---|
| 1 | Miles → Kilometres | × 1.60934 | 5 mi = 8.05 km |
| 2 | Kilometres → Miles | × 0.62137 | 10 km = 6.21 mi |
| 3 | Pounds → Kilograms | × 0.45359 | 180 lb = 81.6 kg |
| 4 | Kilograms → Pounds | × 2.20462 | 75 kg = 165.3 lb |
| 5 | Fahrenheit → Celsius | (°F − 32) × 5/9 | 72°F = 22.2°C |
| 6 | Celsius → Fahrenheit | (°C × 9/5) + 32 | 25°C = 77°F |
| 7 | Feet → Metres | × 0.3048 | 6 ft = 1.83 m |
| 8 | Metres → Feet | × 3.28084 | 2 m = 6.56 ft |
| 9 | Inches → Centimetres | × 2.54 | 10 in = 25.4 cm |
| 10 | Centimetres → Inches | × 0.3937 | 30 cm = 11.81 in |
| 11 | US Gallons → Litres | × 3.78541 | 5 gal = 18.93 L |
| 12 | Litres → US Gallons | × 0.26417 | 20 L = 5.28 gal |
| 13 | Ounces → Grams | × 28.3495 | 4 oz = 113.4 g |
| 14 | Grams → Ounces | × 0.03527 | 100 g = 3.53 oz |
| 15 | Square feet → Square metres | × 0.0929 | 1,000 sq ft = 92.9 m² |
| 16 | Square metres → Square feet | × 10.7639 | 50 m² = 538.2 sq ft |
| 17 | mph → km/h | × 1.60934 | 70 mph = 112.7 km/h |
| 18 | km/h → mph | × 0.62137 | 80 km/h = 49.7 mph |
| 19 | Stone → Kilograms | × 6.35029 | 10 st = 63.5 kg |
| 20 | Acres → Hectares | × 0.4047 | 10 acres = 4.05 ha |
Mental Arithmetic Shortcuts
When a calculator is not available, these rough approximations are accurate enough for most everyday purposes:
- Miles to km: Multiply by 1.6 (or add 60%). 10 miles ≈ 16 km.
- km to miles: Multiply by 0.6 (or subtract 40%). 10 km ≈ 6 miles.
- kg to lb: Multiply by 2.2. 50 kg ≈ 110 lb.
- lb to kg: Divide by 2.2. 200 lb ≈ 90 kg.
- °C to °F: Double and add 30. 20°C → 40 + 30 = 70°F. (Actual: 68°F — close enough for weather.)
- °F to °C: Subtract 30 and halve. 70°F → 40 ÷ 2 = 20°C. (Actual: 21.1°C.)
- Litres to US gallons: Divide by 3.8. 20 L ≈ 5.3 gal.
- Inches to cm: Multiply by 2.5. 10 in ≈ 25 cm. (Actual: 25.4 cm.)
For the full background on the metric and imperial systems and why they differ, read our complete guide to unit conversion.
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