Aisha K.
Mar 12, 2026
Clean layout and the results update instantly. Exactly what I needed for a quick planning check.
Unit Converters
Inches to Millimeters Converter (in to mm)
Inches
Going the other way? Open the reverse converter
in → mm
25.4 mm
1 in = 25.4 mm. 2 in = 50.8 mm. A 12 in ruler is 304.8 mm.
- You typed
- 1 in
- One mm is
- 0.0394 in
- How it’s calculated
- millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.
Inches to Millimeters conversion table
Common in values in mm. Same factor as the converter above: millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.
| Inches | Millimeters |
|---|---|
| 0.25 in | 6.35 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 12 in | 304.8 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
Plain-English guide
Terms & how it works
Confused by a field? Read the short definitions here while you use the tool.
Inches
The “Inches” value used in this tool’s formula. Adjust it to see results update live.
millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.
The international inch is exactly 25.4 mm. That 1959 agreement is why a 1/4 in bolt is 6.35 mm, not “about 6.” Use this when a US drawing meets a metric mill. Fractions of an inch still need you to divide the fraction first.
How this calculator works
The international inch is exactly 25.4 mm. That 1959 agreement is why a 1/4 in bolt is 6.35 mm, not “about 6.” Use this when a US drawing meets a metric mill. Fractions of an inch still need you to divide the fraction first. millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover. Scenario: 1 in = 25.4 mm. 2 in = 50.8 mm. A 12 in ruler is 304.8 mm.
millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.
Scenario: 1 in = 25.4 mm. 2 in = 50.8 mm. A 12 in ruler is 304.8 mm.
When to use this Inches to Millimeters
Common use cases
- The international inch is exactly 25.4 mm. That 1959 agreement is why a 1/4 in bolt is 6.35 mm, not “about 6.” Use this when a US drawing meets a metric mill. Fractions of an inch still need you to divide the fraction first.
- Sanity-check with this scenario: 1 in = 25.4 mm. 2 in = 50.8 mm. A 12 in ruler is 304.8 mm.
- The relationship is: millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.
Localized examples
- Unit Converters: the example on this page uses the same formula as the widget.
What you get
- Fields: Inches
- millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.
- Scenario on the page: 1 in = 25.4 mm. 2 in = 50.8 mm. A 12 in ruler is 304.8 mm.
How to Convert Inches to Millimeters
- 1Enter Inches. Use the values you have, not a catalog average, unless that is all you know.
- 2millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.
- 3Scenario: 1 in = 25.4 mm. 2 in = 50.8 mm. A 12 in ruler is 304.8 mm.
- 4Check which dictionary the other person is using — US or UK, decimal or 1,024 — then trust the number.
Governing formula
millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.
1 in = 25.4 mm. 2 in = 50.8 mm. A 12 in ruler is 304.8 mm.
1 in = 25.4 mm. 2 in = 50.8 mm. A 12 in ruler is 304.8 mm.
Variable definitions
- value
Inches
The “Inches” field. Default 1; typical range 0–1000000000.
- The conversion (millimeters = inches × 25.4. Exact by definition, not a rounded survey leftover.) does not pick US vs UK gallons, SI vs binary megabytes, or Mach at altitude for you. Read the footnote on the page.
- Nothing here is uploaded for the calculation itself.
Frequently Asked Questions
No. 1 in = 25.4 mm exactly since the international yard and pound agreement.
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- Millimeters to InchesWrench sizes, phone specs, and rain totals often arrive in mm. Hardware aisles in the US still think in fractions of an inch. Divide mm by 25.4. A “25 mm” socket is not 1 inch; it is 0.984 in.
- BMI Metric and ImperialBMI = kg / m² = 703 × lb / in². Same index, two unit systems. It does not know muscle, bone, or why a powerlifter and a couch get the same number. Categories are public-health bins, not a diagnosis.
- Bra Size ConverterBand in inches (US/UK) and cup letter. EU bands are centimeters rounded to 5 (34 → 75). Cup letters drift after D: UK DD vs US DD/E is a forum war. Sister sizes (34C / 32D) share cup volume, not this converter’s job.
- Centimeters to InchesHeight charts, inseam tables, and sewing patterns swap cm and inches constantly. Divide cm by 2.54. A 180 cm person is about 5 ft 11 in — the leftover 0.16 in is why both sides of a doorway argue about the last fraction.
- Centimeters to Pixelspx = (cm / 2.54) × DPI. A 10 cm bar at 300 DPI is 1,181 px. A4 width 21 cm at 300 DPI is 2,480 px. Packaging die-lines still want millimeters and bleed; this is the raster step.
- Cubic Inches to Cubic CentimetersEngine displacement: a “350” small-block is 350 in³, about 5.7 L (5,735 cc). Multiply in³ by 16.387. One liter is 1,000 cm³. This is why 5.0 L and 302 in³ show up on the same valve cover.
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Reviews & Ratings
See what others think about this tool, then leave your own rating to help improve CalculioHub.
4.8
out of 5.0
4 reviews
Daniel R.
Feb 28, 2026
Very usable on mobile. Would love a save/export option later, but the math feels solid.
Priya S.
Feb 3, 2026
The FAQ section answered my questions before I even had to search. Smooth dark mode too.
Marcus L.
Jan 19, 2026
Simple inputs, clear outputs. This replaced three bookmarks I used to juggle.
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