Calculator – Feet & Inches Conversion To Millimetres, Centimetres and Metres

Free Online Calculator to Convert Feet / Inches To Metric Measurements

Using our free online calculator, you can convert feet, inches and sub inches into metric measurements such as millimeters and metres.

Article By: Tom Ayre | Last Update: November 2020

Imperial measurements found on old drawings or from parts of the world that still use imperial can be a pain. Converting the numbers to a more usable format can sometimes be tricky, especially for the more modern generations!

Amazingly, there are still 3 countries that by default still use imperial measurements. These are:

  • United States of America
  • Liberia
  • Myanmar

Using our online feet and inches calculator you can quickly convert measurements to metric in the form of metres, centimetres and millimetres.

You can find the calculator below, we also show you how to calculate the measurements manually!

How to Calculate and Convert From Feet & Inches By Hand

In this calculation I will show you how to convert 2 feet, 3 inches, 5/16ths to millimetres.

Step 1
Work out how many feet you have and multiply this number by 12 to convert it into inches. For instance here we have 2 feet, so this equals 24 inches (as there are 12 inches to a foot).

Step 2
Work out how many inches you have and add this to the number you worked out in step 1. Here we have 3 inches, so the total inches equals 24 + 3 which equal 27.

Step 3
Convert to millimetres by multiplying by 25.4. So if we have 27 inches, multiply it by 25.4 to equal 685.8 mm.

Step 4
If you have sub inches then work out the number of sub inches you have in the form of a fraction of sixteenths i.e 1/16, 2/16 etc. Multiply the number at the beginning or top of the fraction by 1.5875. So if you have 5/16ths the calculation is 5 x 1.5875. This equals 7.9375 mm.

Step 5
Add up everything, so from step 3 we have 685.8 and from step 4 we have 7.9375. Added together this makes 693.7375mm, or 69.374cm, 0.694m.

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