Length Converter — mm, cm, Metres, Inches & Feet
Convert millimetres, centimetres, metres, inches and feet for UK building and site measurements. Free instant length converter with all results shown together.
Enter your measurements
How this length converter works
The converter changes every input to metres first, then calculates the equivalent value in millimetres, centimetres, metres, inches and feet using fixed unit relationships.
1 inch = 25.4 mm
1 foot = 12 inches = 0.3048 m
Worked examples
4 inches = 101.6 mm.
8 feet = 2.4384 m.
Common building conversions
Millimetres to metres
Divide by 1,000. For example, 150 mm = 0.15 m and 2,400 mm = 2.4 m.
Inches to millimetres
Multiply inches by 25.4. For example, 4 in = 101.6 mm and 6 in = 152.4 mm.
Feet to metres
Multiply feet by 0.3048. For example, 8 ft = 2.4384 m and 10 ft = 3.048 m.
Why unit consistency matters on site
A small unit mistake can create a very large quantity error when measurements are multiplied into areas or volumes. Convert all dimensions into compatible units before using them in a calculator. This is especially important when changing a depth such as 100 mm into metres before a cubic-metre calculation.
Once the length units are consistent, use the Floor Area Calculator, Wall Area Calculator or Cubic Metre Calculator for the next stage.
Using the unit-code field
Enter the measurement value, then use 1 for mm, 2 for cm, 3 for metres, 4 for inches or 5 for feet. The calculator keeps the output in decimal form so the converted values can be copied directly into quantity calculations.
Exact and rounded conversions
The relationships 1 inch = 25.4 mm and 1 foot = 0.3048 m are exact definitions. The displayed results are rounded for readability, so avoid repeatedly converting a rounded result back and forth when precision matters. Keep the original measurement and convert from that source value.
Common conversion mistakes
- Entering 100 mm as 100 m in an area or volume calculation.
- Treating a decimal-foot result as feet-and-inches notation.
- Rounding a converted dimension too early before multiplying it.
- Mixing imperial and metric dimensions in the same quantity formula.
- Confusing linear units with square or cubic units.
Measurement tool only. This converter changes units; it does not add tolerances, waste allowances or product-specific dimensions.
Frequently asked questions
How many millimetres are in a metre?
There are exactly 1,000 millimetres in one metre.
How many millimetres are in an inch?
One inch is exactly 25.4 millimetres.
How many metres are in a foot?
One foot is exactly 0.3048 metres.
How do I convert millimetres to metres?
Divide the millimetre value by 1,000. For example, 250 mm = 0.25 m.
How do I convert feet to metres?
Multiply the number of feet by 0.3048. For example, 10 ft = 3.048 m.
Does this converter use feet and inches together?
No. It uses decimal feet and decimal inches so the values can be reused directly in calculations.
Related measuring tools
Need to convert area rather than length? Use the Area Converter. For m²-to-linear-metre calculations, use the Linear Metre Calculator, or return to the Measuring & Conversions hub.