To measure millimeters, you typically use a ruler or metric stick. However, if you don't have these tools, there are some ways to estimate the number of millimeters. Likewise, if you know the measurement in a different unit of length, you can convert the value to millimeters.
Method 1 of 4: Measuring millimeters
Step 1. Look at the unmarked lines on a measuring ruler
Numbered lines represent centimeters, but unmarked lines represent millimeters.
- If a measuring ruler is too small, you can also use a measuring tape. Small unnumbered lines on the measuring tape that fall between the numbered ones must represent millimeters.
- Note that every 1 centimeter is equal to 10 mm.
Step 2. Place the "0" end of the ruler on the starting edge
Position the ruler so that the tip of the "0" aligns with the starting point of the edge or line you want to measure.
The ruler may not have a "0" marked on it. If this is the case, be aware that the "0" is simply the tip of the border that comes directly before the "1" mark on the ruler
Step 3. Read the numbered mark immediately before the final edge
Find the point where the edge or line you are measuring ends. Locate the numbered centimeter mark just before that point and then multiply that number by 10 to determine the millimeter equivalent.
- Keep the ruler straight and flat when placed against the line you are measuring.
- If the border ends in a marked number line, you can multiply that value by 10 and get your final answer.
For example: the length of one of the line measurements goes from 0 to the 2 mark, so the line is 20 (2 x 10) mm long
Step 4. Count the unnumbered lines after the last numbered mark
Count the number of millimeter marks between the last numbered mark you just identified and the actual endpoint of the object to be measured.
Step 5. Add the two values to calculate the length in millimeters
The sum of your converted centimeters and extra millimeters value will equal the total number of millimeters your measured border or line length.
- For example: a line extends from mark 0 to the fifth line after mark 7: so the length is 75 mm.
- 7 x 10 = 70.
- 70 + 5 = 75.
Method 2 of 4: Estimating millimeters
Step 1. Find an item approximately 1 millimeter long
The simplest item to use would be a plastic ID card, document, credit card or library card. These plastic cards are usually about 1 mm thick from front to back.
A plastic card is probably the easiest product to use. Other items that are about 1 millimeter long or wide tend to be more difficult to use, but may include a grain of sand or salt, 10 sheets of stapled notebook paper, the thickness of a sheet of heavy printing paper, a thickness of a fingernail, the thickness of a grain of rice, etc
Step 2. Place the object to be measured on a blank sheet of paper
Place the edge or line you plan to measure on the white or clear sheet of paper. Try to keep the entire edge on the paper.
- If desired, you can use a pencil to trace outside the edge. This allows you to remove the object being measured and only work with a straight line, which will make it easier to measure these short lengths. But that's just optional.
- Paper needs to be light in color. If not, you may have a hard time seeing your marks.
Step 3. Mark the starting edge
Use a pencil to carefully mark a perpendicular line on the side of the edge you are measuring. This will be your starting edge.
Step 4. Place the measurement item on the starting edge
Place the narrow 1mm edge of your plastic card onto the paper, placing it along your starting edge line. Draw another small mark with your pencil on the opposite side of the card.
- Keep the mark as close to the outside edge of your card as possible.
- Note that you can use this procedure for any other estimating tool. It is not exclusive to plastic ID cards.
Step 5. Move the measurement item below the full length
Slide the card so that it is outside your newly created tag. Then draw another mark on the opposite side of the card again. Continue to move the card down the line in small increments like this, marking each one, until you reach the end of the edge you are measuring.
- Keep the card perpendicular to the line being measured as long as you measure the marks.
- Also mark the end of the line.
Step 6. Count the gaps
Remove the edge being measured and the card you are using to measure it. Count the gaps between each line you marked. The number of gaps will provide your estimate of the number of millimeters.
Just count the spaces, not the lines, as there will be one more
Method 3 of 4: Converting Other Metric Measures to Millimeters
Step 1. Convert centimeters to millimeters
There are 10 millimeters in every 1 centimeter.
- When you know the size of an object in centimeters but need to figure out the length in millimeters, multiply the number of centimeters by 10.
- For example: 2, 4 cm x 10 = 24 mm.
Step 2. Calculate the number of millimeters from the number of meters
For every meter there are 1,000 millimeters.
- If you need to know the length of something in millimeters, but receive the measurement in meters, multiply the number of meters by 1000 to find the equivalent value in millimeters.
- Example: 5.13 m x 1000 = 5.130 mm.
Step 3. Determine the number of millimeters when you have kilometers
There are 1,000,000 millimeters in every km.
- To change the recorded length measurement in kilometers to a value in millimeters, you must multiply the number of kilometers by 1,000,000.
- For example: 1.4 km x 1000000 = 1,400,000 mm.
Method 4 of 4: Converting Imperial Units to Millimeters
Step 1. Convert inches to millimeters
If you are given a measurement in inches, you can convert it to millimeters by dividing it by a conversion factor of: 0.039370
- There are 25, 4 mm in 1 inch. This isn't a constant ratio, however, which is why you need to use a conversion factor instead of adding 25.4 millimeters for every inch.
- For example: 9, 3 inches / 0, 039370 = 236, 22 millimeters.
Step 2. Determine the number of millimeters from the number of feet (feet)
To find an equal value of millimeters when you know the size of something in feet, you would divide the number of feet by a conversion factor of: 0.0032808
For example: 4.7 feet / 0.0032808 = 1432.58 mm
Step 3. Calculate millimeters from yards
When you receive a yardage measurement but need to convert it to millimeters, you can do so by dividing the yardage by a conversion factor of: 0, 0010936.