The inch is the standard unit of length in the imperial system of measurement. If you're trying to measure in inches, it's best to use a tool specifically designed for measuring inches. Fortunately, even if you don't have a tool of this type, there are ways to estimate and/or convert other units of measurement to inches.
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Method 1 of 4: Using Measuring Tools
Step 1. Make sure you use a measuring tool that uses inches
The inch is usually found on a yard ruler, or tape measure. The size of the object to be measured will determine the best tool for you.
- For example, use a measuring stick if you're trying to measure the length of something straight and flat-sided. Rulers are best suited for short distances, while yardsticks are ideal for objects that are 0.3-1 meters long.
- Use a tape measure when you need to measure the distance around a curved object. The measuring tape can be bent making it suitable for objects that are neither flat nor straight.
Step 2. Notice how the gauge divides the inches into fractions
Count the number of small lines between the numbered lines on the measuring device. Since each numbered line represents an inch, the number of lines between them indicates how the tool breaks the inch into fractions.
- If there is 1 unnumbered line, the inch is split in half.
- If there are 3 unnumbered lines, the inches are split into.
- If there are 7 unnumbered lines, the inches are split into.
- If there are 15 unnumbered lines, the inch is broken down to 1/16.
Step 3. Align the tip of the measuring tool with the tip of the object you want to measure
Place the starting end of the measuring device (numbered “0”) at the nearest end of the object or distance you want to measure. Make sure the starting end of the measuring tool is perfectly aligned with the end of the object for the most accurate measurement.
If the starting end of the gauge doesn't have a “0” number, you can also determine this by looking for the number “1”. The number "0" on the tip of the gauge is before the number line "1"
Step 4. Expand the measuring tool according to the length of the object being measured
Bring the measuring device to the object you want to measure. Always keep the measuring tool parallel to the length of the object to ensure accurate results.
- When in use, the measuring stick should lie flat against the edge or line being measured.
- If using a tape measure, this tool must cover the entire distance being measured.
Step 5. Determine the last full inch number on the tool that measures the object
This is the last numerical value on the measuring instrument before it reaches the other end of the line, edge, or distance being measured. This number is the full inch value of the measured length.
The numbers on a ruler, yardstick, or tape measure all represent the full inch value. The short unnumbered line between the numbered lines is a fraction of an inch
Step 6. Count the number of unnumbered lines from the last full inch digit
Determine the number of unnumbered lines on the measuring instrument until the line is exactly parallel to the distance or object being measured. Then, count the number of unnumbered lines between the last full inch value and the line at the end, including the end line itself.
Step 7. Add up the fractions you just calculated to the full inch value
Thus, the fraction just calculated is included with the full inch value. If you have, you will get the final measurement value of the measured line/distance/edge. Make sure you've determined how the gauge divides the inch into fractions, before doing this.
- For example, if the measured object stops on the fifth line of a total of 7 lines after the number “3”, it means that the length of the object is 3 inches plus inch.
- If the end of the object being measured lands exactly on the number line, you don't need to add a fraction.
Method 2 of 4: Estimating Inches
Step 1. Find a 1 inch long object that can be used to estimate the length
The most common object used to estimate 1 inch is an adult thumb, which is usually 1 inch wide. Other options include a water bottle cap, a removable pencil eraser, a standard rubber eraser width, a paper clip length, and a standard small sewing pin length.
The distance between the top knuckle of the thumb and the tip of the thumb of an adult hand is also usually about 1 inch
Step 2. Trace the length of whatever object you measured on a piece of paper
Place the edge you want to measure on a blank white sheet of paper. Use a pencil to trace the length of the edges from one end to the other.
- The line traced onto the paper should be the same length as the edge of the object you want to measure. After tracing the edges, you can take things out of the paper.
- Make sure that you use white or bright paper so that the markings you are going to make can be clearly seen.
Tip: If the object you want to measure is longer than the paper, you can also reverse this step by tracing the 1-inch long object on a piece of paper. Then, you can use the trace to estimate the length of the object you want to measure.
Step 3. Place an inch-long object at the beginning of the traced line, then mark the end of the object
Align one end of the object used for estimating inches with the end of the traced line. Mark the end of the measuring object using a pencil on the paper.
For example, if you are using your thumb, lay it horizontally over the line, with the end of your thumb parallel to the starting point of the line. Then, use a pencil to mark a line just above the thumb
Step 4. Move the measuring object so that its initial tip is at the last mark
Move the object on the line so that its starting point is parallel to the line you created earlier. As before, make a mark at the end of the measuring object.
Step 5. Repeat this process until you have finished marking the length of the entire line
Each time you shift the position of the measuring object, make sure the edge of the gauge is parallel to the line. If the distance of the remaining line is much smaller than the length of the measuring object, just estimate the size of the fraction by eye.
For example, if the final distance is about half the length of the measuring object, the remaining distance is inch
Step 6. Calculate the amount of distance between each line to make an estimate
After reaching the end of the line, lift the measuring object. Count the number of gaps between each mark. The total is an approximation of the inches measured.
- Count the amount of space between the lines, and not the lines themselves.
- Make sure you calculate the distance before the first line as well as the distance after the last line.
Method 3 of 4: Converting Other Imperial Units to Inches
Step 1. Convert feet to inches by multiplying by 12
One foot equals 12 inches. So, to convert the measurement in feet to inches, multiply by 12.
For example, if you measure 5 feet, multiply by 12 to get 60 inches
Step 2. Convert yards to inches by multiplying by 36
One yard equals 36 inches. If your number is in yards, multiply by 36 to get the measurement in inches.
For example, if an object is 2 yards long, multiply by 36 to get 72 inches
Step 3. Find the inches based on the number of miles
In one mile there are 63,360 inches. If a distance is known in miles, multiply by 63,360 to get its equivalent in inches.
For example, if you know a distance of 0.5 miles, multiply by 63,360 to get the distance in inches, which is 31680 inches
Method 4 of 4: Converting Metric Units to Inches
Step 1. Calculate inches from millimeters by multiplying 0.03937
Every 1 millimeter is equal to 0.03937 inch. Multiply the length value in millimeters by the conversion factor of 0.03937 to convert it to inches.
For example, if you have a measurement of 92 millimeters long, multiply by 0.03937 to get 3.62 inches
Step 2. Convert centimeters to inches by multiplying by 0, 3937
One centimeter is equal to 0.3937 inches. To find inches of distance measured in centimeters, multiply by the conversion factor, which is 0.3937.
For example, if you have a size of 34.18 centimeters, multiply by 0.3937 to get a value of 13.46 inches
Step 3. Determine the number of inches from the number of meters
One meter equals 39.37 inches. If a length is measured in meters, you can convert it to inches by multiplying it by a conversion factor of 39, 37.
