cm to Inches Converter
Convert centimetres and inches with optional feet-and-inches results.
Free converter
Unit Converter
Convert between Metric (SI), US Customary, and UK Imperial units across length, mass/weight, volume, area, speed, and fixed time intervals using official NIST conversion factors.
Conversions run in your browser. Entered and converted numbers are not placed in the URL or analytics.
How to use this tool
Select a measurement category (Length, Mass / Weight, Volume, Area, Speed, or Time), choose your From and To units, and enter a finite number and select Convert to calculate inside your browser.
For dedicated height and dimension conversions (with automatic feet-and-inches output), open the cm to Inches Converter.
For body weight, gym plates, and luggage (with UK stones-and-pounds output), open the kg to lb Converter.
For Celsius (°C), Fahrenheit (°F), and Kelvin (K), open the Temperature Converter.
For calendar months and leap-year dates (which do not use fixed 30-day multipliers), use the Date Calculator or Days Between Dates Calculator.
Transparent method: base-unit conversion method
To prevent rounding drift when converting between multiple units, this tool converts every input to its category reference unit first—using the exact defining constants published in the National Institute of Standards and Technology (NIST) Guide to the SI (SP 811)—before converting out to your target unit:
| Category | SI Base / Reference Unit | Exact Defining Constants Used (NIST SP 811) |
|---|---|---|
| Length | Metre (m) | 1 inch = 0.0254 m (exact); 1 foot = 0.3048 m (exact); 1 yard = 0.9144 m (exact); 1 international mile = 1,609.344 m (exact) |
| Mass / Weight | Kilogram (kg) | 1 avoirdupois pound (lb) = 0.45359237 kg (exact); 1 oz = 28.349523125 g; 1 stone = 6.35029318 kg (14 lbs) |
| Volume (Liquid & Cubic) | Litre (L) / Cubic Metre (m³) | 1 US gallon = 3.785411784 L (exact 231 in³); 1 UK Imperial gallon = 4.54609 L (exact); 1 US cup = 236.5882365 mL |
| Area | Square Metre (m²) | 1 sq foot = 0.09290304 m² (exact); 1 acre = 4,046.8564224 m² (43,560 sq ft); 1 hectare = 10,000 m² |
| Speed | Metres per second (m/s) | 1 km/h = 0.277777... m/s (1 ÷ 3.6); 1 mph = 0.44704 m/s (exact); 1 knot = 0.514444... m/s (1,852 m/h) |
| Time (Fixed Duration) | Second (s) | 1 minute = 60 s; 1 hour = 3,600 s; 1 day = 86,400 s; 1 week = 604,800 s |
Quick-reference sheet: common everyday metric ↔ imperial conversions
Bookmark this table (or add it to your Reference folder using our 7-folder browser bookmark system) for kitchen, DIY, travel, and fitness conversions:
| Category | Metric Unit | US Customary / Imperial Equivalent | Reverse Conversion (Imperial → Metric) |
|---|---|---|---|
| Length | 1 centimetre (cm) | 0.3937 inches | 1 inch = 2.54 cm (exact) |
| Length | 1 metre (m) | 3.2808 feet (3 ft 3.37 in / 1.0936 yards) | 1 foot = 0.3048 m (30.48 cm) |
| Length | 1 kilometre (km) | 0.6214 miles | 1 mile = 1.609344 km (1,609.34 m) |
| Mass / Weight | 1 gram (g) | 0.03527 ounces (oz) | 1 ounce (oz) = 28.3495 g |
| Mass / Weight | 1 kilogram (kg) | 2.20462 pounds (lbs) | 1 pound (lb) = 0.453592 kg (453.59 g) |
| Mass / Weight | 1 metric tonne (t) (1,000 kg) | 2,204.62 lbs (1.1023 US short tons) | 1 US short ton (2,000 lbs) = 907.185 kg |
| Volume | 1 millilitre (mL) | 0.03381 US fl oz (0.2029 US tsp) | 1 US teaspoon = 4.9289 mL (~5 mL culinary) |
| Volume | 100 millilitres (mL) | 3.3814 US fl oz (3.5195 UK Imp fl oz) | 1 US fl oz = 29.5735 mL (1 UK fl oz = 28.4131 mL) |
| Volume | 1 litre (L) (1,000 mL) | 4.2268 US cups (1.0567 US quarts) | 1 US Customary cup = 236.59 mL (240 mL FDA label) |
| Volume | 1 litre (L) | 0.2642 US gallons (0.2200 UK Imp gallons) | 1 US gallon = 3.7854 L (1 UK gallon = 4.5461 L) |
| Area | 1 square metre (m²) | 10.7639 square feet (sq ft) | 100 sq ft = 9.2903 m² |
| Area | 1 hectare (ha) (10,000 m²) | 2.4711 acres | 1 acre = 0.4047 hectares (4,046.86 m²) |
| Speed | 100 km/h | 62.1371 mph | 60 mph = 96.5606 km/h |
| Fuel Economy | 1 km per litre (km/L) | 2.3521 US MPG (2.8248 UK MPG) | Test full trip fuel costs in the Fuel Cost Calculator |
3 critical unit differences between the US, UK, and Canada
When ordering materials, following recipes, or comparing car specs across the United States, the United Kingdom, and Canada, watch out for three units that share the same name but hold different amounts:
US Liquid Gallon (3.785 L) vs. UK Imperial Gallon (4.546 L): An Imperial gallon is 20.1% larger than a US gallon (1 Imperial gallon = 1.20095 US gallons). Likewise, a UK Imperial pint (568.26 mL / 20 Imp fl oz) is 20% larger than a US liquid pint (473.18 mL / 16 US fl oz).
US Cups (236.59 mL) vs. UK/Canadian Metric Cups (250 mL) vs. Vintage Imperial Cups (284.13 mL): If you are baking across borders, check our full breakdown of US cups vs. UK cups recipe measurement differences before measuring liquid or flour.
US Short Ton (2,000 lbs), UK Long Ton (2,240 lbs), and Metric Tonne (2,204.62 lbs):
US Short Ton: 2,000 lbs (907.185 kg)
Metric Tonne (t): 1,000 kg (2,204.62 lbs)
UK Imperial Long Ton: 2,240 lbs (1,016.05 kg, or 160 stone)
Assumptions and limits
- Length uses the international inch, foot, yard and mile; mass uses the international avoirdupois pound.
- US customary and British Imperial volume units are labelled separately and never treated as interchangeable.
- A day is exactly 24 hours and a week is exactly 7 days in this fixed-duration converter; variable calendar months and years are excluded.
- Temperature is excluded from this factor engine because it requires offset formulas; use the focused Temperature Converter for Celsius, Fahrenheit and Kelvin.
- The engine keeps full JavaScript number precision internally; display formatting limits noise without rounding intermediate values.
- Negative finite values are accepted as mathematical conversions even when a negative physical measurement may not describe a practical quantity.
Sources
Frequently asked questions
Why is 1 inch equal to exactly 2.54 centimetres?
In 1959, the national standards laboratories of the United States, the United Kingdom, Canada, Australia, New Zealand, and South Africa signed the International Yard and Pound Agreement, defining the international yard as exactly 0.9144 metres—which makes 1 inch (1/36 of a yard) equal to exactly 2.54 centimetres (25.4 millimetres).
What is the difference between a US fluid ounce and a UK Imperial fluid ounce?
One US fluid ounce is 29.5735 millilitres (1/128 of a US gallon), whereas one UK Imperial fluid ounce is slightly smaller at 28.4131 millilitres (1/160 of an Imperial gallon). However, because a UK pint contains 20 fluid ounces while a US pint contains 16 fluid ounces, a UK pint is larger overall (568 mL vs. 473 mL).
Why doesn't the Time unit converter include months and years?
Seconds, minutes, hours (3,600 s), days (86,400 s), and weeks (604,800 s) have fixed mathematical lengths. Calendar months vary between 28 and 31 days and calendar years vary between 365 and 366 days, so month and year math should always be done in a date-aware tool like the Date Calculator or Days Between Dates Calculator.
How do I convert square feet to square metres when measuring an apartment or room?
Multiply square feet by 0.09290304 to get square metres (or divide square feet by 10.7639). For example, a 500-square-foot studio apartment equals 46.45 square metres—helpful when planning furniture layouts in our guide on how to declutter a small space.
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