How to convert millimeters to inches
To convert millimeters to inches, multiply the number of millimeters by 0.03937 (or divide by 25.4).
Example: 25 mm = 0.98425 in.
Common for tools, bolts, rainfall and camera lenses.
Millimeters to Inches conversion chart
| mm | in |
|---|---|
| 0.5 mm | 0.01969 in |
| 1 mm | 0.03937 in |
| 2 mm | 0.07874 in |
| 3 mm | 0.11811 in |
| 4 mm | 0.15748 in |
| 5 mm | 0.19685 in |
| 6 mm | 0.23622 in |
| 7 mm | 0.27559 in |
| 8 mm | 0.31496 in |
| 9 mm | 0.35433 in |
| 10 mm | 0.3937 in |
| 12 mm | 0.47244 in |
| 15 mm | 0.59055 in |
| 20 mm | 0.7874 in |
| 25 mm | 0.98425 in |
| 30 mm | 1.181 in |
| 40 mm | 1.575 in |
| 50 mm | 1.969 in |
| 60 mm | 2.362 in |
| 70 mm | 2.756 in |
| 75 mm | 2.953 in |
| 80 mm | 3.15 in |
| 90 mm | 3.543 in |
| 100 mm | 3.937 in |
| 150 mm | 5.906 in |
| 200 mm | 7.874 in |
| 250 mm | 9.843 in |
| 500 mm | 19.685 in |
| 1,000 mm | 39.37 in |
Metric vs. U.S. customary units
The United States uses U.S. customary units — inches, feet, miles, pounds, gallons and degrees Fahrenheit — for most everyday purposes. Canada officially adopted the metric system in the 1970s, so road signs, weather forecasts, gas pumps and food labels use kilometers, degrees Celsius, liters and grams. In practice many Canadians still use feet and inches for height, pounds for body weight and square feet for homes, which is why conversions come up constantly on both sides of the border.
Exact conversion factors
Since 1959 the inch, foot, yard, mile and pound have been defined in metric terms, so these conversions are exact, not approximations:
- 1 inch = 2.54 cm exactly, so 1 foot = 30.48 cm and 1 mile = 1.609344 km.
- 1 pound = 0.45359237 kg exactly; 1 ounce = 28.349523125 g.
- 1 U.S. gallon = 3.785411784 liters. The imperial gallon used in the U.K. is larger: 4.54609 liters.
- 1 acre = 4,046.8564224 m², and 1 hectare = 10,000 m² (about 2.471 acres).
Temperature is different because the scales have different zero points: °F = °C × 9/5 + 32 and °C = (°F − 32) × 5/9. Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level, and −40 is the same in both scales.
Quick mental shortcuts
- Kilometers to miles: multiply by 0.6 (100 km ≈ 60 miles; the exact figure is 62.1).
- Kilograms to pounds: double it and add 10% (70 kg → 140 + 14 = 154 lb).
- Celsius to Fahrenheit: double it and add 30 for a rough estimate (20 °C → 70 °F; the exact answer is 68 °F).
- Liters to U.S. gallons: divide by 4 for a quick estimate (40 L ≈ 10 gallons; exactly 10.57).
Cooking and recipe conversions
U.S. recipes measure by volume — cups, tablespoons and teaspoons — while Canadian and most international recipes use milliliters and grams. A U.S. cup is about 237 mL, but Canadian "metric" measuring cups hold 250 mL, so the difference adds up in baking. For flour, sugar and butter, weighing in grams is more accurate than cups because the density of each ingredient differs.
Popular conversions
Pick a conversion below for a dedicated page with the formula, worked examples and a complete conversion chart.
Tips for accurate conversions
Keep full precision until the final step and round only the answer — rounding intermediate numbers can add noticeable errors, especially in recipes, construction and engineering. Always check which gallon, ounce or ton a source means: U.S. and imperial units share names but not sizes, and a "fluid ounce" measures volume while an "ounce" of weight measures mass. For temperatures, remember that a temperature difference converts differently from a temperature reading: a change of 10 °C equals a change of 18 °F, without adding 32.
Popular unit conversions
- Centimeters to Inches
- Inches to Centimeters
- Feet to Meters
- Meters to Feet
- Kilometers to Miles
- Miles to Kilometers
- Millimeters to Inches
- Inches to Millimeters
- Yards to Meters
- Meters to Yards
- Kilograms to Pounds
- Pounds to Kilograms
- Grams to Ounces
- Ounces to Grams
- Celsius to Fahrenheit
- Fahrenheit to Celsius
- Liters to Gallons
- Gallons to Liters
- Milliliters to Fluid Ounces
- Fluid Ounces to Milliliters
- Cups to Milliliters
- Milliliters to Cups
- Square Feet to Square Meters
- Square Meters to Square Feet
- Acres to Hectares
- Hectares to Acres
- Miles Per Hour to Kilometers Per Hour
- Kilometers Per Hour to Miles Per Hour
Frequently asked questions
How many centimeters are in an inch?
How do I convert kg to pounds?
What is the formula for Celsius to Fahrenheit?
Is a U.S. gallon the same as a Canadian gallon?
How many square feet are in a square meter?
Sources & methodology
This calculator was last reviewed on November 2, 2026. Figures are based on the following official and primary sources:
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