Unit Converter Guide — Length, Weight, Speed & Area
Whether you're following a recipe that uses grams instead of ounces, trying to understand how fast 100 km/h is in miles per hour, or converting a room's square footage to square meters for a flooring estimate, unit conversion is one of the most practical everyday math skills. This guide covers the most common conversions across length, weight, speed, and area — with quick reference tables and the formulas behind them.
Metric vs Imperial — The Big Picture
Most of the world uses the metric system (meters, kilograms, liters) while the United States primarily uses the imperial system (feet, pounds, gallons). The United Kingdom uses a mix of both. Understanding which system a measurement belongs to is the first step in any conversion.
Key insight: Metric units always relate by powers of 10 — a kilometer is exactly 1,000 meters, a kilogram is exactly 1,000 grams. Imperial units have irregular relationships (12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile) which is why conversion is trickier.
Length Conversions
Length is the most frequently converted unit type. Here are the key relationships and a quick reference table:
| From | To | Multiply By |
|---|---|---|
| Inches | Centimeters | 2.54 |
| Centimeters | Inches | 0.3937 |
| Feet | Meters | 0.3048 |
| Meters | Feet | 3.2808 |
| Miles | Kilometers | 1.60934 |
| Kilometers | Miles | 0.62137 |
| Yards | Meters | 0.9144 |
| Meters | Yards | 1.09361 |
Common Length Reference Points
- 1 inch = 2.54 cm (exact)
- A standard door is about 2 meters (6.6 feet) tall
- A football field is 100 yards (91.4 meters)
- A marathon is 26.2 miles (42.195 km)
- 5 feet 10 inches = 177.8 cm
Weight Conversions
Weight conversions come up constantly in cooking, shipping, and health contexts. The US uses pounds and ounces; most of the world uses kilograms and grams.
| From | To | Multiply By |
|---|---|---|
| Pounds (lb) | Kilograms (kg) | 0.45359 |
| Kilograms (kg) | Pounds (lb) | 2.20462 |
| Ounces (oz) | Grams (g) | 28.3495 |
| Grams (g) | Ounces (oz) | 0.03527 |
| Stone | Pounds (lb) | 14 |
| Stone | Kilograms (kg) | 6.35029 |
| Metric tons | Pounds (lb) | 2,204.62 |
Quick Weight Reference Points
- 1 pound = 16 ounces = 453.6 grams
- 1 kilogram ≈ 2.2 pounds
- A 150 lb person weighs about 68 kg
- A British stone = 14 pounds = 6.35 kg
Speed Conversions
Speed conversions matter for travel, sports, and science. The most common conversion is between miles per hour (mph) used in the US and UK, and kilometers per hour (km/h) used almost everywhere else.
| From | To | Multiply By |
|---|---|---|
| MPH | KPH | 1.60934 |
| KPH | MPH | 0.62137 |
| MPH | Meters/sec | 0.44704 |
| KPH | Meters/sec | 0.27778 |
| Knots | MPH | 1.15078 |
| Knots | KPH | 1.852 |
Common Speed Reference Points
- 60 mph = 96.6 km/h (US highway speed)
- 100 km/h = 62.1 mph (European highway speed)
- The speed of sound = 767 mph = 1,235 km/h
- A fast recreational cyclist averages about 15 mph (24 km/h)
- World record 100m sprint speed ≈ 27.8 mph (44.7 km/h)
Area Conversions
Area conversions are essential for real estate, gardening, flooring, and land measurement. Note that area units are squared, so a meter is 3.28 feet but a square meter is 10.76 square feet.
| From | To | Multiply By |
|---|---|---|
| Square feet | Square meters | 0.09290 |
| Square meters | Square feet | 10.7639 |
| Acres | Square feet | 43,560 |
| Acres | Hectares | 0.40469 |
| Hectares | Acres | 2.47105 |
| Square miles | Square km | 2.58999 |
| Square km | Square miles | 0.38610 |
Common Area Reference Points
- A typical US home is about 2,300 sq ft (214 sq meters)
- A football field is about 1.32 acres (0.53 hectares)
- 1 acre = roughly the size of an American football field
- Manhattan is about 22.83 square miles (59 square km)
Convert any unit instantly with our free unit converter — length, weight, speed, and area all in one place.
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