Measuring millimeters is typically done using a metric ruler or a specialized measuring tool. If you don't have a measuring device on hand, there are other ways to determine length in millimeters. Additionally, if you have a measurement in another unit, you can easily convert it to millimeters.

How to Measure Millimeters

Step 1. Identify the unmarked lines on your ruler.

Step 1

Take note of the unmarked lines on the ruler. The numbered lines indicate centimeters, while the unmarked ones represent millimeters.

  • If you have a short ruler, you can use the measuring tool — the small ticks between the numbered lines also correspond to millimeters.
  • Remember that 1 cm equals 10 mm.

Step 2. Place the "0" end of the ruler at the starting edge.

Step 2

Position the "0" end of the ruler at the starting point. Ensure that the ruler is straight and parallel to the line you are about to measure.

  • If the ruler doesn't have a "0" mark, use the edge that is right before the "1" mark.

Step 3. Locate the numbered line before the edge of the object being measured.

Step 3

Look for the numbered line that is directly in front of the end of your object. Remember this mark, then multiply it by 10 to get the value in millimeters.

  • Ensure the ruler is lying flat on the surface.
  • If the edge ends at a numbered line, simply multiply that number by 10. For example, if the length from 0 to 2 cm is measured, that equals 20 mm (2 * 10).

Step 4. Count the unnumbered ticks after the last numbered mark.

Step 4

Count the unnumbered ticks between the last numbered line and the endpoint of the object being measured.

Step 5. Add both values to get the length in millimeters.

Step 5

Add the two obtained values to find the total length in millimeters. The sum of the centimeter value and the additional millimeters will give you the final result.

  • For instance, if the length from 0 to 5 ticks after 7 cm is measured, then that equals 75 mm: 7 * 10 = 70 and 70 + 5 = 75.

Approximate Measurement in Millimeters

Step 1. Find an item that is about 1 mm in size.

Step 1

Choose an item that is roughly equal to 1 mm. This could be a plastic card, ID, or credit card, as they usually have a thickness of about 1 mm.

  • Plastic cards are an excellent choice. Small items like grains of salt or sand, 10 sheets of paper, the thickness of a single sheet of printer paper, the thickness of a fingernail, or a grain of rice can also work.

Step 2. Place the item on a clean sheet of paper.

Step 2

Lay the object on a light sheet of paper so that its edge is on the paper. Try to ensure that the entire edge is on the surface.

  • You can draw a line along the edge with a pencil to make subsequent measurements easier, but this is not necessary.
  • Ensure the paper is light-colored so the lines are clearly visible.

Step 3. Mark the starting edge.

Step 3

Use a pencil to carefully mark a line perpendicular to the edge of the item being measured. This will be your starting point.

Step 4. Position the measuring item at the starting mark.

Step 4

Place the narrow edge of the measuring item next to the starting mark on the paper. Again, draw a small tick on the opposite side.

  • Try to get as close as possible to the edge of the item.
  • This method is suitable for other objects, not just plastic cards.

Step 5. Move the measuring item along the entire length.

Step 5

Slide the item along the line, marking a new point each time until you reach the end of the object being measured.

  • Ensure the item is perpendicular to the line.
  • Don’t forget to mark the endpoint.

Step 6. Count the intervals.

Step 6

Remove the measuring item and count the number of intervals between the marks. This number will give you an approximate value in millimeters.

  • Count only the intervals; ignore the lines.

Converting Other Metric Units to Millimeters

Step 1. Convert centimeters to millimeters.

Step 1

To convert centimeters to millimeters, remember: there are 10 millimeters in one centimeter.

  • Multiply the number of centimeters by 10 to get millimeters. For example, 2.4 cm * 10 = 24 mm.

Step 2. Convert meters to millimeters.

Step 2

There are 1000 millimeters in one meter.

  • Multiply the number of meters by 1000 to get millimeters. For example, 5.13 m * 1000 = 5130 mm.

Step 3. Determine millimeters from kilometers.

Step 3

There are 1,000,000 millimeters in one kilometer.

  • Multiply kilometers by 1,000,000 to convert to millimeters. For example, 1.4 km * 1,000,000 = 1,400,000 mm.

Converting Imperial Units to Millimeters

Step 1. Convert inches to millimeters.

Step 1

To convert inches to millimeters, divide by the conversion factor 0.039370.

  • There are 25.4 mm in one inch. Use the conversion factor for accuracy. For example, 9.3 inches / 0.039370 = 236.22 mm.

Step 2. Convert feet to millimeters.

Step 2

To convert feet to millimeters, divide the number of feet by the factor 0.0032808.

  • For example, 4.7 feet / 0.0032808 = 1432.58 mm.

Step 3. Convert yards to millimeters.

Step 3

To convert yards to millimeters, divide the number of yards by the factor 0.0010936.

  • For example, 0.03 yards / 0.0010936 = 27.43 mm.