What this tool does
Length is the most converted unit family there is: a floor plan in feet, a road sign in miles, a package dimension in centimetres, a bolt specification in millimetres. Most converters handle the popular pairs and lose precision on the rest, often by routing the value through a rounded intermediate unit. This one works from the exact international definitions, in both directions, from millimetre to mile.
How it works
Every unit in the metric and imperial length systems is defined as an exact multiple of the metre. One inch is exactly 2.54 centimetres, which makes one foot exactly 30.48 centimetres and one yard exactly 0.9144 metres. The statute mile is 1,609.344 metres and the nautical mile is 1,852 metres. Because these factors are fixed by international agreement rather than measured, a conversion adds no uncertainty of its own — only the precision that went into the input.
Converting between two units divides by the first factor and multiplies by the second in a single step. Centimetres to inches divides by 2.54, and inches to centimetres multiplies by it. Doing the calculation in one pass instead of routing the value through metres or another intermediate keeps every digit the input actually carries, which matters when the number is a specification rather than an estimate. The reverse direction is the same factor inverted, so both directions round the same way.
Compound measures are treated as their own case rather than as two separate conversions. Centimetres to feet needs both the inch factor and the twelve inches in a foot, and the answer comes back as whole feet plus the remainder in inches as well as a decimal, because 5.91 ft is harder to picture than 5 ft 10.87 in. The reference table behind the tool lists every factor used, so any result can be checked by hand against the same definition.
Worked example
Converting 180 cm to inches and to feet and inches.
- 180 ÷ 2.54 = 70.8661 inches
- 70.8661 ÷ 12 = 5.9055 feet
- Remainder = 70.8661 - 60 = 10.8661 inches
180 cm = 70.87 in = 5 ft 10.87 in. Reversing it, 5 ft 11 in is 71 × 2.54 = 180.34 cm.
Accuracy and limitations
- Factors are exact by international agreement, so any rounding in a result comes from the input and the display precision, not from the conversion itself.
- Length only. Area needs the factor squared and volume needs it cubed, and this tool does not apply those powers.
- For legal, medical or trade measurement, use the official conversion standard for your jurisdiction.
Frequently asked questions
- How many centimetres are in an inch?
- Exactly 2.54 cm, the international definition since 1959. That single factor also makes one foot 30.48 cm and one yard 91.44 cm exactly, with no approximation anywhere in the chain.
- How do I convert cm to inches?
- Divide by 2.54. 180 cm ÷ 2.54 = 70.87 inches, which is 5 feet 10.87 inches once you divide by 12 and keep the remainder.
- How do I convert feet to meters?
- Multiply by 0.3048, because one foot is exactly 30.48 cm. Six feet is 1.8288 m, and converting back divides by the same number, so no precision is lost in either direction.
- How many kilometres are in a mile?
- One mile is 1.609344 km exactly, so one kilometre is 0.621371 miles. The everyday rounding of 1.6 km per mile is close enough for estimating a drive but not for a specification.
- What is the difference between a mile and a nautical mile?
- A statute mile is 1,609.344 metres, while a nautical mile is 1,852 metres, defined as one minute of latitude for navigation. A nautical mile is about 1.15 statute miles, so sea and road distances never match.
- How many inches are in a foot?
- Twelve, exactly — the foot-to-inch relationship involves no decimal at all. To split a total of inches into feet and inches, divide by 12 and use the remainder as the inches.