Unit Converter
Convert between different units of measurement instantly and accurately.
Understanding Unit Conversions
Unit conversion is essential for science, engineering, cooking, travel, and everyday life. Different countries and industries use different measurement systems, making conversion tools indispensable.
Measurement Systems
Metric System (SI)
Used by most of the world, the metric system is based on powers of 10, making conversions simple:
- Length: meter (m), kilometer (1000m), centimeter (0.01m), millimeter (0.001m)
- Weight: kilogram (kg), gram (0.001kg), milligram (0.000001kg), ton (1000kg)
- Volume: liter (L), milliliter (0.001L)
- Temperature: Celsius (°C), Kelvin (K) for science
Imperial System
Used primarily in the United States, the imperial system has irregular conversion factors:
- Length: mile, yard (3 feet), foot (12 inches), inch
- Weight: pound (16 ounces), ounce
- Volume: gallon (4 quarts), quart (2 pints), pint (2 cups), cup (8 fl oz), fluid ounce
- Temperature: Fahrenheit (°F)
Common Conversion Factors
Length Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| Meters | Feet | 3.28084 | 10m = 32.81 ft |
| Kilometers | Miles | 0.621371 | 10km = 6.21 mi |
| Inches | Centimeters | 2.54 | 10in = 25.4 cm |
| Miles | Kilometers | 1.60934 | 10mi = 16.09 km |
Weight/Mass Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| Kilograms | Pounds | 2.20462 | 10kg = 22.05 lbs |
| Pounds | Kilograms | 0.453592 | 10lbs = 4.54 kg |
| Ounces | Grams | 28.3495 | 10oz = 283.50 g |
| Pounds | Ounces | 16 | 10lbs = 160 oz |
Temperature Conversions
Temperature conversions require formulas rather than simple multiplication:
Celsius ↔ Fahrenheit
- °F = (°C × 9/5) + 32
- °C = (°F - 32) × 5/9
Examples:
- 0°C = 32°F (freezing point of water)
- 100°C = 212°F (boiling point of water)
- 37°C = 98.6°F (human body temperature)
- 25°C = 77°F (comfortable room temperature)
Celsius ↔ Kelvin
- K = °C + 273.15
- °C = K - 273.15
Kelvin is used in science because it starts at absolute zero (the coldest possible temperature). Water freezes at 273.15K and boils at 373.15K.
Volume Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| Liters | Gallons (US) | 0.264172 | 10L = 2.64 gal |
| Gallons (US) | Liters | 3.78541 | 10gal = 37.85 L |
| Milliliters | Fluid Ounces | 0.033814 | 100mL = 3.38 fl oz |
| Cups | Milliliters | 236.588 | 2 cups = 473.18 mL |
Speed Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| km/h | mph | 0.621371 | 100 km/h = 62.14 mph |
| mph | km/h | 1.60934 | 60 mph = 96.56 km/h |
| m/s | km/h | 3.6 | 10 m/s = 36 km/h |
| knots | km/h | 1.852 | 100 knots = 185.2 km/h |
Practical Conversion Tips
Cooking & Recipes
- 1 cup = 240 mL (approximate, US measurement)
- 1 tablespoon = 15 mL
- 1 teaspoon = 5 mL
- Oven: 350°F = 175°C = 180°C (fan-forced)
- 450°F = 230°C (high heat)
Travel & Navigation
- Speed limits: 65 mph ≈ 105 km/h, 100 km/h ≈ 62 mph
- Fuel efficiency: 30 mpg ≈ 7.8 L/100km
- Distance: 1 mile ≈ 1.6 km, 1 km ≈ 0.6 miles
- Quick estimate: 5 miles ≈ 8 km
Body Measurements
- Height: 6 feet = 183 cm, 5'5" = 165 cm
- Weight: 150 lbs ≈ 68 kg, 70 kg ≈ 154 lbs
- Body temperature: 98.6°F = 37°C
- Fever: > 100.4°F (38°C)
Mental Math Shortcuts
Quick Distance Estimates
- Miles to km: Multiply by 1.6 (or use 8/5 for precision)
- Km to miles: Multiply by 0.6 (or use 5/8 for precision)
- Feet to meters: Divide by 3 (actually 3.28, but close)
Quick Weight Estimates
- Lbs to kg: Divide by 2 (actually 2.2, so slightly over)
- Kg to lbs: Multiply by 2 (actually 2.2, so slightly under)
Quick Temperature Estimates
- °C to °F: Double and add 30 (close approximation)
- °F to °C: Subtract 30 and halve (close approximation)
- Precise: °F = (°C × 1.8) + 32
Why Different Systems Exist
The metric system was developed in France in the 1790s based on scientific principles and powers of 10. It became the international standard because of its simplicity. The imperial system evolved from various English units over centuries, with measurements originally based on body parts (foot, inch) and everyday objects.
The United States primarily uses imperial units due to the cost and complexity of conversion. Most other countries switched to metric in the 20th century. Science globally uses metric (SI units) for consistency.
Frequently Asked Questions
How do I convert between metric and imperial units?
Select the category (length, weight, etc.), choose your starting unit (e.g., kilometers), enter the value, then select the target unit (e.g., miles). Our calculator instantly converts between metric and imperial systems using precise conversion factors.
What is the difference between Celsius, Fahrenheit, and Kelvin?
Celsius is used globally, with 0°C as freezing and 100°C as boiling. Fahrenheit (US) has 32°F freezing and 212°F boiling. Kelvin is used in science, starting at absolute zero (0K = -273.15°C). Water freezes at 273.15K and boils at 373.15K.
How many feet are in a meter?
1 meter equals approximately 3.28 feet (3.28084 to be exact). This is one of the most common conversions. Conversely, 1 foot equals 0.3048 meters or 30.48 centimeters.
How do I convert pounds to kilograms?
1 pound equals 0.453592 kilograms. To convert pounds to kg, multiply by 0.453592. To convert kg to pounds, multiply by 2.20462. For example: 150 lbs = 68.04 kg, and 70 kg = 154.32 lbs.
What is the difference between weight and mass?
Mass measures the amount of matter (kg, g) and stays constant. Weight measures gravitational force (Newtons) and varies by location. On Earth, we often use the terms interchangeably. Our calculator converts mass units (kg, lbs, etc.), which is what scales measure.
How many liters are in a gallon?
1 US gallon equals 3.78541 liters. 1 liter equals 0.264172 US gallons. Note: UK (imperial) gallons are larger at 4.54609 liters. Our calculator uses US gallons by default.
Can I convert between different types of units (e.g., length to weight)?
No, you can only convert within the same category. Length converts to length, weight to weight, etc. You cannot convert kilometers to kilograms because they measure different physical properties. However, temperature can be converted between Celsius, Fahrenheit, and Kelvin.
Are your conversion factors accurate?
Yes, we use official conversion factors defined by international standards (ISO, NIST). All calculations are precise to 6 decimal places, which is more than sufficient for everyday use and most professional applications.
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