Step-by-Step Formula: How Unit Conversion Works
Unit conversion uses a two-step process through a "base unit." Every unit in a category is defined by its relationship to one base unit. To convert from unit A to unit B:
Step 1: Convert value from unit A → base unit
Step 2: Convert base unit → unit B
For example, converting 5 miles to kilometers: Miles → meters (base) → kilometers. 5 miles × 1609.344 m/mile = 8046.72 meters. Then 8046.72 m ÷ 1000 m/km = 8.047 km.
Temperature is the exception—it uses formulas instead of simple ratios because the scales don't share a zero point. Celsius to Fahrenheit: °F = °C × 9/5 + 32. Celsius to Kelvin: K = °C + 273.15.
Common Conversion Reference Table
| From | To | Multiply by |
|---|---|---|
| 1 mile | kilometers | 1.609 |
| 1 inch | centimeters | 2.54 |
| 1 pound | kilograms | 0.4536 |
| 1 ounce | grams | 28.35 |
| 1 US gallon | liters | 3.785 |
| 1 US cup | milliliters | 236.6 |
| 1 square foot | square meters | 0.0929 |
| 1 acre | hectares | 0.4047 |
| 1 mph | km/h | 1.609 |
Common Mistakes
- Confusing US and Imperial gallons. A US gallon (3.785 L) is smaller than an Imperial gallon (4.546 L). UK fuel economy numbers look better because their gallons are bigger.
- Using weight instead of mass. Pounds measure force on Earth; kilograms measure mass. On the Moon, you'd weigh 1/6 as many pounds but the same kilograms.
- Forgetting that temperature conversion isn't linear. You can't just multiply—you must also add/subtract an offset because Fahrenheit and Celsius have different zero points.
- Mixing up fluid ounces and weight ounces. 8 fluid ounces of honey weighs about 12 weight ounces. Fluid ounces measure volume; ounces measure weight.
- Using decimal vs binary for data. Hard drive manufacturers use decimal (1 GB = 1 billion bytes), but your OS uses binary (1 GB = 1.074 billion bytes). That's why a "500 GB" drive shows as 465 GB.
Frequently Asked Questions
How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit temperature, then multiply by 5/9. For example: 72°F → (72 - 32) × 5/9 = 22.2°C. For a quick mental estimate, subtract 30 and divide by 2 (gives 21°C, close enough for everyday use).
How many cups are in a gallon?
There are 16 US cups in 1 US gallon. A gallon is also 4 quarts, 8 pints, or 128 fluid ounces. For metric: 1 US gallon = 3.785 liters. Note that UK (Imperial) gallons are larger: 1 Imperial gallon = 4.546 liters = about 19.2 US cups.
What is the difference between a US and Imperial gallon?
A US gallon is 3.785 liters, while an Imperial (UK) gallon is 4.546 liters—about 20% larger. This means UK fuel economy figures in MPG are higher than US figures for the same car. This converter uses US measurements.
How do I convert between miles and kilometers?
1 mile = 1.60934 kilometers. To convert miles to km, multiply by 1.609. To convert km to miles, multiply by 0.621. Quick mental math: add about 60% to miles to get km, or take about 40% off km to get miles.
Is a kilobyte 1000 or 1024 bytes?
In computing (binary), 1 KB = 1,024 bytes. In the SI/metric system, 1 kB = 1,000 bytes. This tool uses binary (1024) since that's how operating systems measure storage. To distinguish, the IEC standard uses "kibibyte" (KiB) for 1024 and "kilobyte" (kB) for 1000.
How many ounces are in a pound?
There are 16 ounces in 1 pound (avoirdupois). 1 pound = 453.592 grams = 0.4536 kilograms. For troy ounces (used for precious metals), 1 troy ounce = 31.1 grams, and there are 12 troy ounces in a troy pound.