Introduction
This inches to mm calculator converts inches to millimeters and millimeters to inches. Just type in a number, and the tool shows the converted value. It works with decimals, fractions, and even feet plus inches, so you can use it no matter how your measurement is written.
One inch equals exactly 25.4 millimeters. That is the fixed number this calculator uses for every conversion. You need to switch between these two units often when cutting lumber, sizing bolts, reading a blueprint, or working with parts made in another country. Getting it wrong by even a small amount can lead to parts that do not fit, wasted material, or costly rework on a job site.
The tool also shows a step-by-step breakdown of each conversion so you can see exactly how the answer was found. A quick-reference table of common inch-to-millimeter values is included at the bottom for fast lookups without any typing at all.
How to Use Our Inches to Mm Calculator
Enter a length in inches or millimeters and this calculator will convert it for you. You will get the result in millimeters or inches, a breakdown in meters or feet, and a step-by-step solution.
Pick your conversion direction. Choose "Inches → MM" to convert inches into millimeters. Choose "MM → Inches" to go the other way. You can also hit the "Swap Direction" button to flip your last result into a new input.
Choose your inch format. Select "Decimal" if you want to type a number like 1.5. Select "Fraction" if you want to type a fraction like 3/4 using the whole number, numerator, and denominator fields.
Pick inches or feet + inches. Choose "Inches" to enter inches only. Choose "Feet + In" to enter a value in feet and inches together. This option only shows when converting inches to millimeters.
Type your value. Enter the number you want to convert in the input field. If you are using fraction mode, fill in the whole number, numerator, and denominator boxes.
Set your decimal precision. Use the dropdown to choose how many decimal places you want in your result, from 0 to 6. The default is 4.
Click "Convert" to see your results. The calculator shows your answer in two cards. For inches to mm, you get total millimeters and a meters-plus-millimeters breakdown. For mm to inches, you get total inches and a feet-plus-inches breakdown. You can copy either result with the "Copy" button next to it.
Use quick-select buttons for common values. Click any of the preset inch values like 0.25, 0.5, 1, or 12 to instantly load and convert that number.
Click any row in the reference table. The table at the bottom lists common inch-to-millimeter conversions. Click a row to load that value into the calculator right away.
How to Convert Inches to Millimeters
One inch equals exactly 25.4 millimeters. To convert any inch value to millimeters, you multiply it by 25.4. For example, 2 inches × 25.4 = 50.8 mm. To go the other way, from millimeters to inches, you divide by 25.4.
Why This Conversion Matters in Construction
Builders, carpenters, and tradespeople often need to switch between inches and millimeters. Many tools, materials, and plans use the metric system, while others use imperial measurements. Getting the conversion wrong, even by a small amount, can cause parts not to fit, gaps in joints, or wasted material. Accurate measurement is one of the most important skills on any job site.
Working with Fractions
In construction, inch measurements are usually written as fractions like 1/4", 3/8", or 15/16". This calculator lets you enter fractions directly so you do not have to convert them to decimals first. It handles common denominators like 2, 4, 8, 16, 32, and 64, which are the standard divisions on a tape measure.
Feet and Inches to Millimeters
Longer measurements are often given in feet and inches, such as 5 ft 6 in. This calculator can take feet and inches together and convert the full length into millimeters or meters. There are 12 inches in one foot, so the tool first turns feet into inches, adds any extra inches, then multiplies the total by 25.4.
Common Conversions to Know
A few conversions come up over and over in construction work. A 1/8 inch is 3.175 mm. A 1/4 inch is 6.35 mm. A 1/2 inch is 12.7 mm. And 12 inches, which is one foot, equals 304.8 mm. Knowing these by heart can save time when you are on a ladder or in the middle of a cut.