Unit Conversion Cheat Sheet: The Most Common Conversions You'll Ever Need
Whether you're following a recipe from another country, helping your kid with science homework, sizing up furniture dimensions, or trying to figure out how fast 100 km/h actually is, unit conversions come up constantly. This page is designed to be bookmarked — a single reference for the most common conversions across length, weight, volume, temperature, speed, area, and digital storage, with the formulas you need to do them by hand.
For quick conversions with instant results, use our Unit Converter tool. But when you want to understand the math or need a printable reference, this cheat sheet has you covered.
Length Conversions
Metric Units
| From | To | Multiply By |
|---|---|---|
| Kilometers | Meters | 1,000 |
| Meters | Centimeters | 100 |
| Centimeters | Millimeters | 10 |
| Meters | Millimeters | 1,000 |
Metric ↔ Imperial
| From | To | Multiply By | Example |
|---|---|---|---|
| Inches | Centimeters | 2.54 | 12 in = 30.48 cm |
| Feet | Meters | 0.3048 | 6 ft = 1.83 m |
| Yards | Meters | 0.9144 | 100 yd = 91.44 m |
| Miles | Kilometers | 1.60934 | 5 mi = 8.05 km |
| Kilometers | Miles | 0.62137 | 10 km = 6.21 mi |
| Centimeters | Inches | 0.3937 | 180 cm = 70.87 in |
Quick mental math: 1 inch ≈ 2.5 cm. 1 foot ≈ 30 cm. 1 mile ≈ 1.6 km. 1 km ≈ 0.6 miles. For rough estimates, multiply km by 0.6 to get miles, or miles by 1.6 to get km.
Weight (Mass) Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| Ounces (oz) | Grams (g) | 28.3495 | 8 oz = 226.8 g |
| Pounds (lb) | Kilograms (kg) | 0.45359 | 150 lb = 68.04 kg |
| Kilograms (kg) | Pounds (lb) | 2.20462 | 70 kg = 154.32 lb |
| Grams (g) | Ounces (oz) | 0.03527 | 500 g = 17.64 oz |
| Stones | Kilograms (kg) | 6.35029 | 10 st = 63.5 kg |
| Metric Tons | Pounds (lb) | 2,204.62 | 1 t = 2,204.62 lb |
Quick mental math: 1 kg ≈ 2.2 lb. 1 lb ≈ 450 g. To convert kg to pounds, double it and add 10%. To convert pounds to kg, halve it and subtract 10%.
Volume Conversions
| From | To | Multiply By |
|---|---|---|
| Teaspoons (tsp) | Milliliters (mL) | 4.929 |
| Tablespoons (tbsp) | Milliliters (mL) | 14.787 |
| Fluid Ounces (fl oz) | Milliliters (mL) | 29.5735 |
| Cups (US) | Milliliters (mL) | 236.588 |
| Pints (US) | Liters (L) | 0.47318 |
| Quarts (US) | Liters (L) | 0.94635 |
| Gallons (US) | Liters (L) | 3.78541 |
| Liters (L) | Gallons (US) | 0.26417 |
Cooking shortcut: 1 cup ≈ 240 mL. 1 tablespoon ≈ 15 mL. 1 teaspoon ≈ 5 mL. 1 gallon ≈ 3.8 liters. Note that UK (imperial) pints and gallons are larger than US ones — a UK pint is 568 mL vs. 473 mL for a US pint.
Temperature Conversions
Temperature is the one conversion that isn't a simple multiplication. Here are the formulas:
Fahrenheit to Celsius: °C = (°F − 32) × 5/9
Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Celsius to Kelvin: K = °C + 273.15
Fahrenheit to Kelvin: K = (°F − 32) × 5/9 + 273.15
Quick Reference Table
| Description | °F | °C | K |
|---|---|---|---|
| Absolute zero | −459.67 | −273.15 | 0 |
| Water freezes | 32 | 0 | 273.15 |
| Room temperature | 68–72 | 20–22 | 293–295 |
| Body temperature | 98.6 | 37 | 310.15 |
| Water boils | 212 | 100 | 373.15 |
| Oven (moderate) | 350 | 177 | 450.15 |
| Oven (hot) | 450 | 232 | 505.15 |
Quick mental math for F→C: Subtract 30, then divide by 2. This gives an approximation: 70°F → (70−30)/2 = 20°C (actual: 21.1°C). Close enough for everyday use.
Speed Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| mph | km/h | 1.60934 | 60 mph = 96.56 km/h |
| km/h | mph | 0.62137 | 100 km/h = 62.14 mph |
| km/h | m/s | 0.27778 | 36 km/h = 10 m/s |
| m/s | km/h | 3.6 | 10 m/s = 36 km/h |
| Knots | km/h | 1.852 | 30 knots = 55.56 km/h |
| Knots | mph | 1.15078 | 30 knots = 34.52 mph |
Handy reference: 100 km/h ≈ 62 mph. 60 mph ≈ 97 km/h. The speed of sound is about 343 m/s (1,235 km/h or 767 mph).
Area Conversions
| From | To | Multiply By |
|---|---|---|
| Square feet (ft²) | Square meters (m²) | 0.0929 |
| Square meters (m²) | Square feet (ft²) | 10.7639 |
| Acres | Hectares | 0.4047 |
| Hectares | Acres | 2.4711 |
| Square miles | Square kilometers | 2.58999 |
| Square kilometers | Square miles | 0.38610 |
| Square inches | Square centimeters | 6.4516 |
Real estate context: 1 acre = 43,560 ft². A typical suburban lot is 0.1-0.5 acres. A soccer field is about 1.75 acres. 1 hectare = 10,000 m² (roughly 2.5 acres).
Digital Storage Conversions
| Unit | Abbreviation | Bytes | Practical Context |
|---|---|---|---|
| Byte | B | 1 | A single character of text |
| Kilobyte | KB | 1,000 | A short email |
| Megabyte | MB | 1,000,000 | A high-res photo (3-8 MB) |
| Gigabyte | GB | 1,000,000,000 | A feature-length movie (1-4 GB) |
| Terabyte | TB | 1,000,000,000,000 | ~250,000 photos or ~500 hours of HD video |
| Petabyte | PB | 1,000,000,000,000,000 | ~1,000 TBs — enterprise scale |
SI vs. Binary: Storage manufacturers use SI units (1 KB = 1,000 bytes), while operating systems historically used binary units (1 KiB = 1,024 bytes). This is why a "500 GB" hard drive shows as ~465 GB in your operating system. The difference grows with scale: a "1 TB" drive shows as about 931 GiB.
SI (decimal): 1 KB = 1,000 B 1 MB = 1,000 KB 1 GB = 1,000 MB
Binary (IEC): 1 KiB = 1,024 B 1 MiB = 1,024 KiB 1 GiB = 1,024 MiB
Bits vs. Bytes: 1 Byte = 8 bits
Internet speeds are measured in bits/sec: 100 Mbps = 12.5 MB/sec
Common Conversions for Everyday Life
A few conversions that come up frequently in daily life, all in one place:
| Scenario | Conversion |
|---|---|
| Height: 5'10" in metric | 177.8 cm (1.778 m) |
| Weight: 160 lb in metric | 72.6 kg |
| Driving: 65 mph in metric | 104.6 km/h |
| Oven: 375°F in Celsius | 190.6°C |
| Weather: 30°C in Fahrenheit | 86°F (hot summer day) |
| Cooking: 2 cups in mL | 473 mL |
| Fuel: 30 mpg in L/100km | 7.84 L/100km |
For instant conversions with any value, use our Unit Converter — just pick a category, enter your number, and see all conversions at once.
Frequently Asked Questions
Why do the US, UK, and other countries use different measurement systems?
The metric system was developed in France in the 1790s and has since been adopted by virtually every country. The US is one of only three countries (along with Myanmar and Liberia) that hasn't officially adopted metric as its primary system. The UK uses a hybrid — metric for most things, but imperial for road distances (miles), body weight (stones/pounds), and beer (pints). Historical inertia, the cost of conversion, and cultural familiarity keep the older systems alive.
What's the difference between a US gallon and a UK gallon?
A US gallon is 3.785 liters. A UK (imperial) gallon is 4.546 liters — about 20% larger. This difference extends through all sub-units: a UK pint is 568 mL vs. 473 mL for a US pint. When following recipes, always check which country's measurements are being used.
How do I convert fuel economy between mpg and L/100km?
The formula is: L/100km = 235.215 ÷ mpg (US). So 30 mpg = 235.215 ÷ 30 = 7.84 L/100km. Note that higher mpg means lower L/100km (they're inversely related). A car getting 40 mpg uses 5.88 L/100km. For UK mpg (imperial gallons), use 282.481 instead of 235.215.
Why is my hard drive smaller than advertised?
Hard drive manufacturers measure capacity in decimal (SI) units: 1 TB = 1,000,000,000,000 bytes. But Windows reports capacity in binary units: 1 TiB = 1,099,511,627,776 bytes. So a "1 TB" drive actually contains 1,000,000,000,000 bytes, which Windows displays as 931 GiB. You're not missing any storage — it's just two different ways of counting the same bytes.