Quick Reference: Common Conversions
| Conversion | Formula | Example |
|---|---|---|
| km → miles | × 0.6214 | 10 km = 6.21 miles |
| miles → km | × 1.6093 | 10 mi = 16.09 km |
| kg → pounds | × 2.2046 | 75 kg = 165.35 lb |
| pounds → kg | × 0.4536 | 150 lb = 68.04 kg |
| cm → inches | × 0.3937 | 180 cm = 70.87 in |
| inches → cm | × 2.54 | 72 in = 182.88 cm |
| °C → °F | (× 9/5) + 32 | 37°C = 98.6°F |
| °F → °C | (− 32) × 5/9 | 98.6°F = 37°C |
Metric vs. Imperial: Who Uses What?
Nearly every country in the world uses the metric system (SI units). The main exceptions are the United States, Myanmar, and Liberia, which officially use imperial/customary units. The UK uses a hybrid system (miles for roads, kg for products).
Temperature Reference Points
| Description | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20–22 | 68–72 | 293–295 |
| Body temperature | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |
Temperature Conversion Formulas
°C to °F: (°C × 9/5) + 32 = °F
Quick estimate °C to °F: Double and add 30. Example: 20°C × 2 + 30 = 70°F (actual: 68°F).
Quick estimate °F to °C: Subtract 30, then halve. Example: 100°F − 30 = 70 ÷ 2 = 35°C (actual: 37.8°C).
Unit Conversions in Cooking
Recipes often mix metric and imperial measurements, especially when sourced internationally. Key cooking conversions:
| From | To | Conversion |
|---|---|---|
| 1 cup | mL | 237 mL |
| 1 tablespoon | mL | 15 mL |
| 1 teaspoon | mL | 5 mL |
| 1 ounce (weight) | grams | 28.35 g |
| 1 pound | grams | 453.6 g |
| 350°F | °C | 177°C |
Unit Conversions for Fitness
Health and fitness use both systems frequently. Body weight is measured in kg or lb, heights in cm or feet/inches, and running distances in km or miles. Here are common fitness conversions:
- 1 mile = 1.609 km. A 5K race is 3.11 miles. A marathon (42.195 km) is 26.22 miles.
- 1 kg = 2.205 lb. So a 70 kg person weighs about 154 lb. Our BMI calculator supports both metric and imperial.
- 1 inch = 2.54 cm. A 5’10” person is 177.8 cm tall. Our body fat calculator uses cm for waist and neck measurements.
If you track calories for weight management, remember that 1 Calorie (food calorie) = 1 kilocalorie (kcal) = 4,184 joules. See our calorie calculator for daily intake recommendations based on your body metrics.
Distance Comparison
Frequently Asked Questions
How to Use This Unit Converter
Select a category (length, weight, volume, temperature, area, speed, etc.), enter a value, and choose the source and target units. The converter handles all common unit conversions.
Formula & How It Works
Each conversion uses standard factors: 1 mile = 1.60934 km, 1 kg = 2.20462 lbs, 1 gallon = 3.78541 liters, 1 acre = 43,560 sq ft.
Calculation Example
5 miles = 8.05 km. 180 lbs = 81.6 kg. 68Β°F = 20Β°C. 2 acres = 87,120 sq ft = 8,094 sq m.
Expert Tips
Quick mental conversions: km to miles β multiply by 0.6. Celsius to Fahrenheit β double and add 30 (rough). 1 meter β 3 feet 3 inches. 1 liter β 1 quart.
How do I quickly convert km to miles in my head?
Multiply by 0.6 for a quick estimate. 100 km ≈ 60 miles. For more accuracy, multiply by 5 and divide by 8: 100 × 5 = 500 ÷ 8 = 62.5 miles (actual: 62.14). Fun fact: the Fibonacci sequence approximates km-to-miles conversions (8 km ≈ 5 miles, 13 km ≈ 8 miles).
What is the quick formula for Celsius to Fahrenheit?
The exact formula is (°C × 9/5) + 32. For a quick estimate: double the Celsius value and add 30. Example: 25°C ≈ 50 + 30 = 80°F (actual: 77°F). This shortcut works well between 0–40°C.
Why does the US still use imperial units?
The US attempted metrication in the 1970s (Metric Conversion Act of 1975), but it was voluntary rather than mandatory, and public resistance was strong. Manufacturing retooling costs and cultural habit have kept imperial units in everyday use. However, US science, medicine, and military largely use metric units.
What is a stone (weight unit)?
A stone is a traditional UK weight unit equal to 14 pounds (6.35 kg). It’s still commonly used in the UK and Ireland for personal body weight. For example, a 170 lb person is 12 stone 2 lb (12 st 2).