Unit Conversion Cheat Sheet: Length, Weight, Area & Temperature
Key conversion factors for inches, feet, miles, pounds, ounces, square feet, acres and °C/°F, plus US vs UK gallons and cups, and common mistakes to avoid.
Recipes from another country, furniture sizes in inches, running routes in kilometers, a weather forecast in Fahrenheit: sooner or later everyone has to convert between metric and imperial units. Students and travelers run into it. So do online shoppers, home cooks, DIY fans and anyone reading a spec sheet written for another market.
This cheat sheet collects the conversion factors you’ll need most often and explains the traps that cause wrong answers, such as US and UK gallons being different sizes. It also shows how to get every conversion at once with a free browser-based converter. For quick checks you can keep the tables below handy. For anything with lots of decimals, let a tool do the math.
Length: inches, feet, miles and their metric equivalents
Length is the most common conversion, and the key numbers are easy to remember. Several of them are exact by definition, not rounded estimates.
| From | To | Multiply by | Notes |
|---|---|---|---|
| 1 inch (in) | centimeters (cm) | 2.54 | Exact by definition |
| 1 foot (ft) | meters (m) | 0.3048 | Exact; 1 ft = 12 in |
| 1 yard (yd) | meters (m) | 0.9144 | Exact; 1 yd = 3 ft |
| 1 mile (mi) | kilometers (km) | 1.609344 | Exact; roughly 1.6 |
| 1 cm | inches | 0.3937 | Rounded |
| 1 m | feet | 3.2808 | Rounded |
| 1 km | miles | 0.6214 | Rounded |
A handy mental shortcut: a kilometer is a bit more than half a mile, so a 10 km race is about 6.2 miles. For heights, remember that 6 feet is about 1.83 m and 5 feet is about 1.52 m.
Weight: pounds, ounces, kilograms and grams
Strictly speaking, pounds and kilograms measure mass, but in everyday use “weight” is fine.
| From | To | Multiply by | Notes |
|---|---|---|---|
| 1 pound (lb) | kilograms (kg) | 0.45359237 | Exact; roughly 0.45 |
| 1 kg | pounds | 2.2046 | Rounded; roughly 2.2 |
| 1 ounce (oz) | grams (g) | 28.3495 | Rounded; roughly 28 |
| 1 g | ounces | 0.03527 | Rounded |
| 1 stone (st) | kilograms | 6.35 | 1 st = 14 lb, used in the UK |
A quick check for body weight or luggage: to go from kilograms to pounds, double the number and add 10%. So 20 kg becomes about 40 + 4 = 44 lb.
The ounce you see here is the weight ounce. It isn’t the same as the fluid ounce, which measures volume. More on that below.
Area: square feet, square meters and acres
Area catches people out because the conversion factor gets squared. A foot is 0.3048 m, but a square foot is 0.3048 × 0.3048 m², not 0.3048 m².
| From | To | Multiply by | Notes |
|---|---|---|---|
| 1 square foot (sq ft) | square meters (m²) | 0.0929 | Rounded |
| 1 m² | square feet | 10.764 | Rounded |
| 1 square inch | square centimeters | 6.4516 | Exact |
| 1 acre | square meters | 4,046.86 | Rounded; 1 acre = 43,560 sq ft |
| 1 acre | hectares (ha) | 0.4047 | 1 ha = 10,000 m² |
| 1 hectare | acres | 2.471 | Rounded |
For apartment listings, a rough rule works well: divide square feet by about 10.8 to get square meters. A 1,000 sq ft home is about 93 m².
Temperature: Celsius and Fahrenheit
You can’t convert temperature with a single multiplier, because the two scales also start from different zero points. Use these formulas:
- Celsius to Fahrenheit: °F = °C × 9/5 + 32
- Fahrenheit to Celsius: °C = (°F − 32) × 5/9
| Celsius | Fahrenheit | What it means |
|---|---|---|
| −40 °C | −40 °F | The one point where both scales match |
| 0 °C | 32 °F | Water freezes |
| 20 °C | 68 °F | Comfortable room temperature |
| 37 °C | 98.6 °F | Typical body temperature |
| 100 °C | 212 °F | Water boils (at sea level) |
| 180 °C | 356 °F | Common oven setting, often written as 350 °F |
For a quick estimate from Celsius, double it and add 30 (so 25 °C ≈ 80 °F; the exact answer is 77 °F). This gets less accurate the further you go from room temperature, so use the real formula for cooking or medical readings.
Volume: why US and UK gallons and cups differ
Volume causes the most confusion, because the US and the UK use the same names for different amounts. The UK system is called “imperial”; the US system is called “US customary.”
| Unit | US size | UK (imperial) size |
|---|---|---|
| Gallon | about 3.785 L | about 4.546 L |
| Pint | about 473 mL | about 568 mL |
| Fluid ounce | about 29.6 mL | about 28.4 mL |
| Cup | about 237 mL (customary); 240 mL on nutrition labels | Traditionally about 284 mL; modern recipes often use a 250 mL metric cup |
A UK gallon is about 20% larger than a US gallon, so fuel-economy figures in “miles per gallon” from the two countries can’t be compared directly. Cups are also tricky. Australian, New Zealand and many Canadian recipes use a 250 mL metric cup, while US recipes use roughly 237 mL. For one cup the gap is small, but it adds up in baking.
How to convert units with Deftivo
The Deftivo unit converter runs entirely in your browser. There’s nothing to install or sign up for, and it shows the result in every unit at once, so you don’t have to pick a target unit first.
- Choose a category: length, weight, area, volume or temperature.
- Type a value and pick its unit. For example, enter 5 and choose feet.
- Read the value in every other unit. The converter lists the equivalent in all the other units in that category, so you can compare meters, centimeters, inches and more side by side.
Because everything appears together, it’s handy for comparing products listed in different units, or for checking a recipe that switches between grams and ounces.
Tips and common mistakes
- Mixing up fluid ounces and weight ounces. A fluid ounce measures volume and a weight ounce measures mass. They only line up roughly for water.
- Assuming a gallon is a gallon. Check whether a recipe, car review or product label is from the US or the UK before converting gallons, pints or fluid ounces.
- Forgetting to square area factors. Converting square feet with the plain foot-to-meter number (0.3048) gives an answer more than three times too big.
- Converting temperature differences with the full formula. A change of 10 °C is a change of 18 °F. Don’t add 32 when you’re converting a difference rather than a reading.
- Rounding too early. Keep full decimals until the final step, especially when you multiply several numbers (area × price per square foot, for example).
- Trusting “1 kg = 2 lb.” It’s close enough for a rough guess, but it’s about 10% off, which matters for shipping limits and dosing.
- Writing units ambiguously. Always write the unit next to the number (“12 in”, “30 cm”) so nobody has to guess later.
FAQ
How many centimeters are in an inch?
Exactly 2.54 centimeters. This value is fixed by international agreement, so it isn’t a rounded figure. To go from centimeters back to inches, divide by 2.54.
What is the formula to convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5 (or 1.8) and add 32. To go the other way, subtract 32 from the Fahrenheit value and multiply by 5/9. For example, 30 °C × 1.8 + 32 = 86 °F.
Why is a UK gallon bigger than a US gallon?
The two countries standardized their measures separately, at different times and from different historical definitions. The imperial gallon is about 4.546 liters and the US gallon is about 3.785 liters. The same difference affects pints and fluid ounces, so always check which system a source uses.
Does the Deftivo unit converter upload my data?
No. The unit converter does its calculations in your browser, so the values you type aren’t sent to a server. You choose a category, enter a value with its unit, and it shows the equivalent in every other unit.