A person who does a lot of measuring on the job will often need to convert metric mm (millimetres) to feet and inches. Regardless of whether the measurements being taken are for building a new cabinet or if they are for laying carpet, it is important to be able to make exact measurements so that the work is done precisely.
Know the length of a millimetre (mm) in inches. The exact length of a mm when expressed as an inch is .0393700787. The number of decimal places you use for the conversion depends on the accuracy wanted. However, if you're converting several measurements, use at least 3 to 4 digits for accurate measurements.
Take a measurement in millimetres. Rulers and tape measures using the metric system have a millimetre scale on them.
Use this measurement for the conversion: Take the measurement in millimetres and multiply it by the number of millimetres in an inch. For example, if there are 100mm, take 100 and multiply it by .0393. The result would be 3.93. Therefore there are 3.93 inches in 100mm.
Know the length of a millimetre in feet. There are .0033 feet in 1mm. Again, to be accurate, use all four decimal places for the conversion.
Take a measurement in millimetres. This measurement could be taken with a tape measure, ruler or yardstick.
Use the measurement to convert the millimetres into feet. To do the conversion, take the millimetres and multiply them by the number of feet in 1mm. For example, if you measured 1,000mm, convert it to feet by taking 1,000 and multiplying it by .0033. The result for this formula would be 3.3 feet.
Take the measurement in millimetres using a tape measure, ruler or yardstick that features metric measurements.
Find one of hundreds of web sites that will automatically do calculations online by searching for "convert mm to feet" or "convert mm to inches" in a search engine.
Enter the number of mm measured in the mm field and select the "convert" button. In the "feet" or "inches" field, there will be the result of how many feet or inches are in the millimetres.
Double check your work. Although this is simple math, mistakes happen.
Estimate as little as possible. When converting millimetres to feet, a small estimate will not make much of a difference if you are only converting the measurement from 20mm, but the higher the number of millimetres, the more the conversion will be off if you estimate.