Unit Conversion Chart
Navigating between metric and imperial systems is a daily challenge for engineers, travelers, cooks, and students. A reliable unit conversion chart saves time and prevents costly mistakes – whether you are translating millimeters to inches for a machining spec or kilograms to pounds at the airport check-in.
Below you will find reference tables for the six most-requested categories, each with precise conversion factors and worked examples.
Length Conversion Chart
Length conversions are the most frequently searched category. The meter is the SI base unit; all other metric length units are decimal multiples or fractions of it.
| From | To | Multiply By |
|---|---|---|
| Millimeters (mm) | Inches (in) | 0.0393701 |
| Centimeters (cm) | Inches (in) | 0.393701 |
| Centimeters (cm) | Feet (ft) | 0.0328084 |
| Meters (m) | Feet (ft) | 3.28084 |
| Meters (m) | Yards (yd) | 1.09361 |
| Kilometers (km) | Miles (mi) | 0.621371 |
| Inches (in) | Millimeters (mm) | 25.4 |
| Inches (in) | Centimeters (cm) | 2.54 |
| Feet (ft) | Meters (m) | 0.3048 |
| Yards (yd) | Meters (m) | 0.9144 |
| Miles (mi) | Kilometers (km) | 1.60934 |
| Nautical miles | Kilometers (km) | 1.852 |
Example: 5 miles = 5 × 1.60934 = 8.0467 km.
The inch-to-millimeter relationship (1 in = 25.4 mm exactly) has been an international standard since 1959, agreed upon by the US, UK, Canada, Australia, New Zealand, and South Africa.
Weight and Mass Conversion Chart
Mass and weight are often treated interchangeably in everyday use, though they differ physically. The kilogram is the SI base unit of mass.
| From | To | Multiply By |
|---|---|---|
| Milligrams (mg) | Ounces (oz) | 0.000035274 |
| Grams (g) | Ounces (oz) | 0.035274 |
| Grams (g) | Pounds (lb) | 0.00220462 |
| Kilograms (kg) | Pounds (lb) | 2.20462 |
| Kilograms (kg) | Stones (st) | 0.157473 |
| Metric tons (t) | US tons | 1.10231 |
| Metric tons (t) | UK tons (long ton) | 0.984207 |
| Ounces (oz) | Grams (g) | 28.3495 |
| Pounds (lb) | Kilograms (kg) | 0.453592 |
| Stones (st) | Kilograms (kg) | 6.35029 |
| US tons | Kilograms (kg) | 907.185 |
Example: 150 lb = 150 × 0.453592 = 68.0388 kg.
Note the three different “tons”: a metric ton (1,000 kg), a US short ton (907.185 kg), and a UK long ton (1,016.05 kg). Specifying which ton you mean avoids errors in shipping and trade.
Volume Conversion Chart
Volume is where US and UK imperial units diverge most noticeably. A US gallon is 3.785 liters; a UK gallon is 4.546 liters – nearly 20% more.
| From | To | Multiply By |
|---|---|---|
| Milliliters (mL) | US fluid ounces (fl oz) | 0.033814 |
| Liters (L) | US quarts (qt) | 1.05669 |
| Liters (L) | US gallons (gal) | 0.264172 |
| Liters (L) | UK gallons (gal) | 0.219969 |
| US fluid ounces | Milliliters (mL) | 29.5735 |
| UK fluid ounces | Milliliters (mL) | 28.4131 |
| US cups | Milliliters (mL) | 236.588 |
| US pints | Liters (L) | 0.473176 |
| UK pints | Liters (L) | 0.568261 |
| US gallons (gal) | Liters (L) | 3.78541 |
| UK gallons (gal) | Liters (L) | 4.54609 |
| Cubic meters (m³) | Liters (L) | 1,000 |
Example: 2 US gallons = 2 × 3.78541 = 7.57082 L.
Cooking and baking are particularly sensitive to US/UK differences. A British recipe calling for “1 pint of milk” expects 568 mL, while an American recipe with “1 pint” means 473 mL.
Temperature Conversion Chart
Temperature is unique because scales have different zero points – you cannot convert by simple multiplication alone.
| Conversion | Formula |
|---|---|
| Celsius to Fahrenheit | °F = °C × 9/5 + 32 |
| Fahrenheit to Celsius | °C = (°F − 32) × 5/9 |
| Celsius to Kelvin | K = °C + 273.15 |
| Kelvin to Celsius | °C = K − 273.15 |
| Fahrenheit to Kelvin | K = (°F − 32) × 5/9 + 273.15 |
| Kelvin to Fahrenheit | °F = (K − 273.15) × 9/5 + 32 |
Quick reference points:
| Description | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20 | 68 | 293.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |
Area Conversion Chart
Area conversions matter in real estate, agriculture, and construction. The hectare (10,000 m²) is standard for land area in metric countries, while the acre dominates in the US and UK.
| From | To | Multiply By |
|---|---|---|
| Square centimeters (cm²) | Square inches (in²) | 0.155000 |
| Square meters (m²) | Square feet (ft²) | 10.7639 |
| Square meters (m²) | Square yards (yd²) | 1.19599 |
| Square kilometers (km²) | Square miles (mi²) | 0.386102 |
| Hectares (ha) | Acres | 2.47105 |
| Square inches (in²) | Square centimeters (cm²) | 6.4516 |
| Square feet (ft²) | Square meters (m²) | 0.0929030 |
| Square yards (yd²) | Square meters (m²) | 0.836127 |
| Square miles (mi²) | Square kilometers (km²) | 2.58999 |
| Acres | Hectares (ha) | 0.404686 |
| Acres | Square feet (ft²) | 43,560 |
Example: 5 acres = 5 × 0.404686 = 2.02343 hectares.
Speed Conversion Chart
Speed conversions come up in automotive, aviation, and weather contexts. Knots (nautical miles per hour) remain standard in maritime and aviation navigation.
| From | To | Multiply By |
|---|---|---|
| m/s | km/h | 3.6 |
| m/s | mph | 2.23694 |
| m/s | Knots (kn) | 1.94384 |
| km/h | m/s | 0.277778 |
| km/h | mph | 0.621371 |
| km/h | Knots (kn) | 0.539957 |
| mph | km/h | 1.60934 |
| mph | m/s | 0.447040 |
| mph | Knots (kn) | 0.868976 |
| Knots (kn) | km/h | 1.852 |
| Knots (kn) | mph | 1.15078 |
Example: 100 km/h = 100 × 0.621371 = 62.1371 mph (typical European highway speed limit).
How to Calculate Any Conversion Manually
Every unit conversion follows one principle: multiply by a conversion factor that relates the two units. The steps are:
- Identify the source unit and target unit. Example: convert 25 cm to inches.
- Find the conversion factor. From the chart above: 1 cm = 0.393701 in.
- Multiply. 25 × 0.393701 = 9.8425 in.
- Check the result roughly. An inch is about 2.5 cm, so 25 cm should be roughly 10 inches – close enough to confirm the math.
For compound units (like km/h to m/s), break the conversion into two steps – convert the length part first, then the time part.
Metric Prefixes Quick Reference
The metric system is decimal-based, so knowing prefixes lets you scale any unit instantly:
| Prefix | Symbol | Factor |
|---|---|---|
| Tera | T | 10¹² (1,000,000,000,000) |
| Giga | G | 10⁹ (1,000,000,000) |
| Mega | M | 10⁶ (1,000,000) |
| Kilo | k | 10³ (1,000) |
| Hecto | h | 10² (100) |
| Deca | da | 10¹ (10) |
| Deci | d | 10⁻¹ (0.1) |
| Centi | c | 10⁻² (0.01) |
| Milli | m | 10⁻³ (0.001) |
| Micro | μ | 10⁻⁶ (0.000001) |
| Nano | n | 10⁻⁹ (0.000000001) |
One kilometer = 1,000 meters; one milligram = 0.001 grams. No exceptions, no irregular forms – this consistency is the metric system’s core advantage over imperial.
This chart is for general reference. For legal, medical, or safety-critical calculations, verify conversion factors against NIST Special Publication 811 or applicable local standards.