Formula used
One international inch equals exactly 25.4 millimeters. This relationship is exact, not an approximation.
How to use this calculator
- Select the required conversion direction.
- Enter a decimal, fraction, mixed number, or scientific value.
- Choose decimal precision and a rounding method.
- Add multiple values inside the batch field when needed.
- Press “Convert values” to view detailed results.
- Copy, print, or export the generated result table.
Common inches to millimeters table
| Inches | Millimeters | Typical fraction |
|---|---|---|
| 0.0625 | 1.5875 | 1/16 |
| 0.125 | 3.175 | 1/8 |
| 0.25 | 6.35 | 1/4 |
| 0.375 | 9.525 | 3/8 |
| 0.5 | 12.7 | 1/2 |
| 0.75 | 19.05 | 3/4 |
| 1 | 25.4 | 1 |
| 2 | 50.8 | 2 |
| 5 | 127 | 5 |
| 10 | 254 | 10 |
| 12 | 304.8 | 12 |
Understanding inches and millimeters
Inches measure length within customary and imperial systems. Millimeters belong to the metric system. Both units appear in manufacturing, construction, printing, and product design.
Decimal inches work well for machining and technical drawings. Fractional inches remain common in workshops and household projects. This calculator accepts both formats without separate fields.
The exact factor prevents conversion drift during repeated calculations. Display rounding changes only the shown result. The unrounded value remains available for verification.
Working with fractional inches
A fraction represents part of one whole inch. For example, one half inch equals 0.5 inches. Multiplying 0.5 by 25.4 produces 12.7 millimeters.
Mixed numbers contain whole and fractional sections. The value 2 3/4 becomes 2.75 inches. Its metric equivalent equals 69.85 millimeters.
Unicode fractions are also accepted for convenience. Values like ½ and ⅜ convert automatically. Invalid denominators receive a clear warning.
Precision and rounding choices
Precision controls how many decimal places appear. Normal rounding selects the nearest displayed value. Upward and downward options support specialized estimating tasks.
Truncation removes extra digits without conventional rounding. This option can suit controlled reporting requirements. Exact output remains visible beside every rounded result.
Scientific notation helps with extremely large or tiny values. Trailing zero removal keeps ordinary results compact. Keep zeros when fixed decimal formatting matters.
Batch conversions and exports
Batch mode processes many measurements together. Separate values using lines, commas, or semicolons. Each valid measurement receives its own result row.
CSV export supports spreadsheets and data workflows. PDF export creates a portable report. Printing offers a simple paper record.
Skipped values appear inside a warning message. Valid entries still complete successfully. This behavior saves time during larger measurement lists.
Frequently asked questions
How many millimeters are in one inch?
One inch contains exactly 25.4 millimeters.
What formula converts inches to millimeters?
Multiply the inch value by 25.4.
Is 25.4 millimeters exactly one inch?
Yes. The international inch is defined as exactly 25.4 millimeters.
Can this calculator convert fractional inches?
Yes. Enter values like 3/8, 2 3/4, or ½.
How many millimeters equal half an inch?
Half an inch equals exactly 12.7 millimeters.
How do I convert millimeters back to inches?
Select reverse conversion, then divide millimeters by 25.4.
Can negative measurements be converted?
Yes. Negative values are supported within the calculator’s safe range.
Why does the result contain decimals?
The metric equivalent often includes fractional millimeters after conversion.
How should millimeter results be rounded?
Choose precision based on your tool, drawing, or reporting requirement.
Can several measurements be converted together?
Yes. Batch mode accepts up to 500 values per request.
Are inch-to-millimeter conversions exact?
The conversion factor is exact. Displayed rounding may shorten the result.