The Ultimate Unit Conversion Guide
Unit conversion is a fundamental skill in science, engineering, cooking, travel, and everyday life. The world uses two major measurement systems — the metric system (used by most of the world) and the imperial/US customary system — and navigating between them confidently can save time, prevent errors, and deepen your understanding of measurements.
Length Conversions
Length is one of the most frequently converted units, especially in international contexts.
Key Conversion Factors
| From | To | Multiply by |
|---|---|---|
| Inches | Centimeters | 2.54 |
| Centimeters | Inches | 0.3937 |
| Feet | Meters | 0.3048 |
| Meters | Feet | 3.2808 |
| Miles | Kilometers | 1.60934 |
| Kilometers | Miles | 0.62137 |
| Yards | Meters | 0.9144 |
Quick Length Reference
- 1 inch = 2.54 cm (exact by definition)
- 1 foot = 30.48 cm
- 5'10" (5 feet 10 inches) = 177.8 cm
- 1 mile = 1.609 km
- A marathon (26.2 miles) = 42.195 km
Use our ⚡ cm to Inches Converter or ⚡ km to Miles Converter.
Weight & Mass Conversions
| From | To | Multiply by |
|---|---|---|
| Pounds (lbs) | Kilograms (kg) | 0.45359 |
| Kilograms (kg) | Pounds (lbs) | 2.20462 |
| Ounces (oz) | Grams (g) | 28.3495 |
| Grams (g) | Ounces (oz) | 0.03527 |
| Stone | Kilograms | 6.35029 |
| Tons (US) | Kilograms | 907.185 |
Practical Weight Examples
- 150 lbs = 68.04 kg
- 70 kg = 154.3 lbs
- 1 cup of all-purpose flour ≈ 120–130 g
- A standard barbell plate (45 lbs) = 20.4 kg
Try our ⚡ kg to lbs Converter for instant weight conversions.
Temperature Conversions
Temperature is the unit type with non-linear conversion formulas — you can't just multiply.
Formulas
Quick Temperature Reference
| Celsius | Fahrenheit | Context |
|---|---|---|
| −40°C | −40°F | The only point where both scales equal |
| 0°C | 32°F | Water freezes |
| 20°C | 68°F | Room temperature |
| 37°C | 98.6°F | Human body temperature |
| 100°C | 212°F | Water boils (at sea level) |
| 180°C | 356°F | Common baking temperature |
Use our ⚡ Celsius to Fahrenheit Converter.
Volume & Liquid Conversions
| From | To | Multiply by |
|---|---|---|
| US Gallons | Liters | 3.78541 |
| Liters | US Gallons | 0.26417 |
| Fluid ounces (fl oz) | Milliliters (ml) | 29.5735 |
| Milliliters (ml) | Fluid ounces | 0.03381 |
| Cups (US) | Milliliters | 236.588 |
| Tablespoons (US) | Milliliters | 14.787 |
| Teaspoons (US) | Milliliters | 4.929 |
Cooking Quick Reference
- 1 cup = 16 tablespoons = 48 teaspoons = 240 ml
- 1 US pint = 2 cups = 473 ml
- 1 US quart = 4 cups = 946 ml
- 1 US gallon = 16 cups = 3.785 liters
Try our ⚡ Liters to Gallons Converter.
Speed Conversions
| From | To | Multiply by |
|---|---|---|
| mph | km/h | 1.60934 |
| km/h | mph | 0.62137 |
| m/s | km/h | 3.6 |
| km/h | m/s | 0.27778 |
| knots | km/h | 1.852 |
Running Pace Reference
- A 10-minute mile = 9.3 min/km = 6.4 km/h
- A 5-minute mile = 4.7 min/km = 12.8 km/h
- World record marathon pace ≈ 2:54/km = 20.7 km/h
Area Conversions
| From | To | Multiply by |
|---|---|---|
| Square feet | Square meters | 0.09290 |
| Square meters | Square feet | 10.7639 |
| Acres | Hectares | 0.40469 |
| Hectares | Acres | 2.47105 |
| Square miles | Square km | 2.58999 |
Tips for Unit Conversion
Use Dimensional Analysis
Chain conversion factors like fractions, canceling units step by step. This prevents errors in multi-step conversions:
Memorize Key Anchors
Instead of memorizing every conversion, memorize a handful of exact ones and derive the rest:
- 1 inch = 2.54 cm (exact)
- 1 kg = 2.205 lbs
- 1 mile = 1.609 km
- 0°C = 32°F
Use Our Converters
For any conversion you need regularly, bookmark the relevant RunCalc converter: Meters to Feet, Inches to cm, and many more.
Conclusion
Unit conversions are essential in a globalized world where metric and imperial systems coexist. Whether you're cooking, traveling, training, building, or studying, this guide and our converter tools have you covered. Bookmark this page and use our calculators whenever you need fast, accurate conversions.