Unit Converter Guide: Every Conversion You'll Ever Need
A practical guide to converting length, weight, temperature, area, and volume units. Learn the most common conversions and when to use them in daily life and work.
Unit conversion is one of those things everyone needs occasionally and nobody wants to memorize. Whether you’re cooking with a foreign recipe, checking a product’s weight for shipping, or understanding a scientific paper, having a reliable unit converter saves time and prevents errors.
Here’s your complete reference guide — plus the most useful conversions to keep in your head.
Length Conversions
Metric to Imperial
| Metric | Imperial | Conversion |
|---|---|---|
| 1 km | 0.621 miles | ÷ 1.609 |
| 1 m | 3.281 feet | × 3.281 |
| 1 m | 1.094 yards | × 1.094 |
| 1 cm | 0.394 inches | × 0.394 |
| 1 mm | 0.039 inches | × 0.039 |
Imperial to Metric
| Imperial | Metric | Conversion |
|---|---|---|
| 1 mile | 1.609 km | × 1.609 |
| 1 yard | 0.914 m | × 0.914 |
| 1 foot | 30.48 cm | × 30.48 |
| 1 inch | 2.54 cm | × 2.54 |
Quick mental math: 1 inch ≈ 2.5 cm, 1 foot ≈ 30 cm, 1 mile ≈ 1.6 km.
Real-world length examples
- Screen size (TV, monitor): always in diagonal inches
- Height: Americans use feet and inches, rest of world uses cm
- Running distances: km (most of world) or miles (US, UK)
- Fabric: meters vs. yards
Weight Conversions
| Unit | Equivalent |
|---|---|
| 1 kg | 2.205 pounds |
| 1 pound | 453.6 grams |
| 1 ounce | 28.35 grams |
| 1 stone | 6.35 kg (14 lbs) — used in UK for body weight |
| 1 metric ton | 1,000 kg = 2,205 lbs |
Quick mental math: 1 kg ≈ 2.2 lbs. So if someone weighs 70 kg, that’s about 154 lbs.
Cooking and baking
- US recipes use cups, tablespoons, teaspoons, ounces
- Most other recipes use grams
- 1 cup of water = 240 ml = 240 g (water is easy; other ingredients vary by density)
- 1 tablespoon = 15 ml; 1 teaspoon = 5 ml
Temperature Conversions
Formulas
Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Fahrenheit to Celsius: °C = (°F − 32) × 5/9
Celsius to Kelvin: K = °C + 273.15
Key reference points
| °C | °F | Situation |
|---|---|---|
| -40 | -40 | Same in both scales |
| 0 | 32 | Water freezes |
| 20 | 68 | Comfortable room temperature |
| 37 | 98.6 | Normal body temperature |
| 100 | 212 | Water boils |
Quick mental estimation: double the Celsius and add 30 to get approximate Fahrenheit. So 25°C ≈ 80°F (actual is 77°F — close enough for everyday use).
Area Conversions
| Unit | Equivalent |
|---|---|
| 1 m² | 10.764 ft² |
| 1 km² | 0.386 square miles |
| 1 hectare (ha) | 10,000 m² = 2.471 acres |
| 1 acre | 4,047 m² |
| 1 평 (Korea) | 3.306 m² |
Real estate context: apartment sizes in Korea are measured in 평 (pyeong). A 30평 apartment is about 99 m² or 1,065 sq ft.
Volume Conversions
Liquid
| Unit | Equivalent |
|---|---|
| 1 liter | 1,000 ml = 0.264 US gallons |
| 1 US gallon | 3.785 liters |
| 1 UK gallon | 4.546 liters |
| 1 US fluid ounce | 29.57 ml |
| 1 cup (US) | 236.6 ml |
Gas context: fuel is sold in liters in most countries, gallons in the US. At $3.50/gallon, that’s about $0.92/liter — useful when comparing fuel costs internationally.
Dry volume
- 1 cup = 16 tablespoons = 48 teaspoons
- Essential for baking conversions between US and metric recipes
Speed Conversions
| km/h | mph | Context |
|---|---|---|
| 60 | 37.3 | City speed limit (typical) |
| 100 | 62.1 | Highway speed limit (metric countries) |
| 120 | 74.6 | Common highway maximum |
| 130 | 80.8 | German Autobahn recommendation |
Formula: km/h × 0.621 = mph; mph × 1.609 = km/h
Digital Storage
| Unit | Bytes |
|---|---|
| 1 KB | 1,024 bytes |
| 1 MB | 1,024 KB |
| 1 GB | 1,024 MB |
| 1 TB | 1,024 GB |
Note: storage manufacturers use decimal (1 GB = 1,000,000,000 bytes), operating systems use binary (1 GB = 1,073,741,824 bytes). That’s why a “1 TB” drive shows as ~931 GB on your computer.
When to Use the Converter (vs. Mental Math)
For rough estimates, mental shortcuts work fine. But use the Unit Converter when:
- Cooking and precision matters (baking especially)
- Engineering, science, or construction calculations
- Shipping and customs (weight limits are strict)
- Medical contexts (drug dosages, body measurements)
- Financial calculations involving units (price per unit, per area, etc.)
The Unit Converter handles length, weight, temperature, area, volume, speed, and more — all in one place, with no ads, no sign-up, completely free.
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