Convert Inches To Millimetres Using The Exact Relationship Of 1 Inch = 25.4 Millimetres. Use Decimal Inches, Whole-And-Fraction Inches, Feet Plus Inches, Or Reverse Millimetres To Inches For Fast Workshop, Construction, Fabrication And Measurement Conversions.
Number Fields Start Blank With A Soft Zero Placeholder. Type Your Measurement And The Zero Is Replaced By Your Entry. The Result Stays Hidden Until You Press Convert Measurement.
Your Result Will Appear Here After You Press Convert Measurement.
The PDF Includes The Conversion Method, Original Measurement, Total Inches, Millimetres, Centimetres And The Exact 25.4 mm-Per-Inch Factor.
Every Inch Contains Exactly 25.4 Millimetres. Multiply The Inch Measurement By 25.4 To Convert It To Metric Millimetres.
Use One Measurement To See Its Equivalent In Millimetres, Centimetres, Metres And Inches.
Uses Exactly 25.4 Millimetres For Every International Inch.
Convert Values Such As 0.5, 2.75 Or 12.125 Inches Directly.
Enter Whole Inches Plus A Numerator And Denominator.
Combine Feet And Remaining Inches Before Converting To Millimetres.
Convert Millimetres Back To Decimal Inches For Cross-Checking.
Save The Original Measurement And Converted Metric Values.
Converting inches to millimetres is a direct multiplication. The international inch is defined as exactly 25.4 millimetres, so there is no estimated or approximate conversion factor required. Multiply the inch value by 25.4 and the result is the equivalent length in millimetres.
Millimetres (mm) = Inches (in) × 25.4
For example, 2 inches × 25.4 = 50.8 mm. A measurement of 6.5 inches converts to 165.1 mm. The same formula works for small workshop dimensions, larger construction measurements and decimal engineering dimensions.
Modern international inch measurements use a fixed relationship to the metric system. This means 25.4 mm is not a rounded classroom shortcut; it is the exact conversion relationship used by the calculator. The displayed result may be rounded to a practical number of decimal places, but the underlying multiplication uses 25.4.
Decimal inches are the simplest input. Enter the number directly and multiply by 25.4. For 3.75 inches:
3.75 × 25.4 = 95.25 mm
Fractional inch dimensions are common on tape measures, fasteners, tools and drawings. Convert the fraction to decimal inches first, add it to any whole-inch value, and then multiply by 25.4.
Total Inches = Whole Inches + (Numerator ÷ Denominator)
For example, 2 3/8 inches = 2 + 3 ÷ 8 = 2.375 inches. Multiply 2.375 by 25.4 to get 60.325 mm.
| Fraction Inch | Decimal Inches | Millimetres | Centimetres |
|---|---|---|---|
| 1/16 in | 0.0625 in | 1.5875 mm | 0.15875 cm |
| 1/8 in | 0.125 in | 3.175 mm | 0.3175 cm |
| 1/4 in | 0.25 in | 6.35 mm | 0.635 cm |
| 3/8 in | 0.375 in | 9.525 mm | 0.9525 cm |
| 1/2 in | 0.5 in | 12.7 mm | 1.27 cm |
| 5/8 in | 0.625 in | 15.875 mm | 1.5875 cm |
| 3/4 in | 0.75 in | 19.05 mm | 1.905 cm |
| 7/8 in | 0.875 in | 22.225 mm | 2.2225 cm |
When a measurement is written in feet and inches, convert the feet portion to inches first. One foot contains 12 inches. Add the remaining inches and multiply the total by 25.4.
Millimetres = ((Feet × 12) + Inches) × 25.4
A length of 5 ft 6 in contains 66 total inches. 66 × 25.4 = 1676.4 mm.
Reverse conversion uses division rather than multiplication. Divide millimetres by 25.4 to obtain decimal inches.
Inches = Millimetres ÷ 25.4
| Inches | Millimetres | Centimetres | Metres |
|---|---|---|---|
| 1 in | 25.4 mm | 2.54 cm | 0.0254 m |
| 2 in | 50.8 mm | 5.08 cm | 0.0508 m |
| 3 in | 76.2 mm | 7.62 cm | 0.0762 m |
| 4 in | 101.6 mm | 10.16 cm | 0.1016 m |
| 6 in | 152.4 mm | 15.24 cm | 0.1524 m |
| 8 in | 203.2 mm | 20.32 cm | 0.2032 m |
| 10 in | 254 mm | 25.4 cm | 0.254 m |
| 12 in | 304.8 mm | 30.48 cm | 0.3048 m |
| 24 in | 609.6 mm | 60.96 cm | 0.6096 m |
| 36 in | 914.4 mm | 91.44 cm | 0.9144 m |
| 48 in | 1219.2 mm | 121.92 cm | 1.2192 m |
Inch-to-millimetre conversion is useful when imperial dimensions need to be compared with metric products, drawings or specifications. Common examples include drill sizes, fasteners, pipe dimensions, timber dimensions, sheet materials, workshop fabrication, imported equipment, concrete formwork measurements and construction details.
Keep enough decimal places for the accuracy of the original measurement and the purpose of the work. A rough site measurement may not justify four decimal places, while a machining or engineering comparison may require greater precision. The exact conversion factor does not make the original measurement more precise than it was.
Australian construction documentation commonly uses metric dimensions, while some imported tools, components and product literature still use inches. Converting those dimensions to millimetres can make it easier to compare them with metric drawings, reinforcement spacing, formwork, fixings and material specifications.
The converter changes units only. It does not determine tolerances, nominal-versus-actual product sizes, fit, clearance, structural adequacy or whether an imperial product is interchangeable with a metric one. Always check the actual product specification when compatibility matters.
Use The Exact Factor And Keep Fraction Handling Separate So The Result Is Easy To Check.
Select Decimal Inches, Fractional Inches Or Feet Plus Inches.
Type The Original Imperial Measurement Without A Prefilled Value.
Use The Exact 25.4 Millimetres Per Inch Relationship.
Match The Final Decimal Precision To The Real Measurement.
These Examples Show The Exact 25.4 mm-Per-Inch Conversion Across Decimal, Fractional And Feet-And-Inches Measurements.
| Input | Total Inches | Calculation | Millimetres | Centimetres |
|---|---|---|---|---|
| 0.5 in | 0.5 in | 0.5 × 25.4 | 12.7 mm | 1.27 cm |
| 2.5 in | 2.5 in | 2.5 × 25.4 | 63.5 mm | 6.35 cm |
| 3 1/2 in | 3.5 in | 3.5 × 25.4 | 88.9 mm | 8.89 cm |
| 7 3/8 in | 7.375 in | 7.375 × 25.4 | 187.325 mm | 18.7325 cm |
| 2 ft 6 in | 30 in | 30 × 25.4 | 762 mm | 76.2 cm |
| 6 ft 0 in | 72 in | 72 × 25.4 | 1828.8 mm | 182.88 cm |
Quick Answers About Inch, Millimetre, Fraction And Feet-And-Inches Conversions.
One International Inch Is Exactly 25.4 Millimetres.
Multiply The Inch Measurement By 25.4.
One-Half Inch Is 0.5 Inches. 0.5 × 25.4 = 12.7 mm.
Divide The Numerator By The Denominator, Add Any Whole Inches, Then Multiply The Total Inches By 25.4.
Yes. Multiply Feet By 12, Add The Remaining Inches, Then Multiply The Total Inches By 25.4.
Divide Millimetres By 25.4.
The Zero Is Only A Placeholder. Typing A Number Replaces It, So The Converter Does Not Add A Leading Zero To Your Entry.
It Is Exact For The International Inch.
Round The Final Result To A Precision Appropriate For The Original Measurement And The Work Being Done.
No. It Converts Length Units Only. Check Actual Product Dimensions, Tolerances And Specifications Separately.
Use Related Converters When You Need To Move Between Common Imperial And Metric Length Units.
Use Recognised Metrology References When Exact Unit Definitions Matter.
United States National Institute Of Standards And Technology Resources On SI Units And Measurement.
Read SI Length InformationInternational Metrology Resources And SI Documentation.
Explore Measurement UnitsCheck Actual Dimensions And Tolerances When Matching Imperial And Metric Components.
Use The Units, Precision And Tolerances Stated In The Controlling Project Documents.