Convert Calibers (cal) to Millimeters (mm)

1 caliber equals 25.4 millimeters.

Formula: mm = cal × 25.4

Caliber to Millimeter Converter

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How to Convert Caliber to Millimeter

1 caliber = 25.4 millimeters

Millimeter = Caliber × 25.4

Example: 1 cal × 25.4 = 25.4 mm

Reverse Conversion

To convert millimeters back to calibers:

  • Remember, 1 millimeter equals 0.0393701 calibers.
  • To convert 25.4 mm to cal, multiply 25.4 x 0.0393701, resulting in 1 cal.

Common Caliber to Millimeter Conversions

Caliber to Millimeter (Part 1)
Caliber Millimeter Actions
1 caliber 25.4 millimeters
5 calibers 127 millimeters
10 calibers 254 millimeters
25 calibers 635 millimeters
Caliber to Millimeter (Part 2)
Caliber Millimeter Actions
50 calibers 1270 millimeters
100 calibers 2540 millimeters
500 calibers 12700 millimeters
1000 calibers 25400 millimeters

Calibers to millimeters Conversion Table

Reference table with common calibers to millimeters conversions. All values calculated with high precision.

Calibers to Millimeters Table
0.0001 to 12

Calibers Millimeters Actions
0.0001 cal 0.00254 mm
0.00025 cal 0.00635 mm
0.0005 cal 0.0127 mm
0.001 cal 0.0254 mm
0.0025 cal 0.0635 mm
0.005 cal 0.127 mm
0.01 cal 0.254 mm
0.025 cal 0.635 mm
0.05 cal 1.27 mm
0.1 cal 2.54 mm
14 cal 6.35 mm
12 cal 12.7 mm

Calibers to Millimeters Table
1 to 100000

Calibers Millimeters Actions
1 cal 25.4 mm
2 12 cal 63.5 mm
5 cal 127 mm
10 cal 254 mm
25 cal 635 mm
50 cal 1270 mm
100 cal 2540 mm
250 cal 6350 mm
500 cal 12700 mm
1000 cal 25400 mm
2500 cal 63500 mm
5000 cal 127000 mm
10000 cal 254000 mm
25000 cal 635000 mm
50000 cal 1270000 mm
100000 cal 2540000 mm

Millimeters to Calibers Table
0.01 to 50

Millimeters Calibers Actions
0.01 mm 0.000393701 cal
0.025 mm 0.000984252 cal
0.05 mm 0.0019685 cal
0.1 mm 0.00393701 cal
14 mm 0.00984252 cal
12 mm 0.019685 cal
1 mm 0.0393701 cal
2 12 mm 0.0984252 cal
5 mm 0.19685 cal
10 mm 0.393701 cal
25 mm 0.984252 cal
50 mm 1.9685 cal

Millimeters to Calibers Table
100 to 10000000

Millimeters Calibers Actions
100 mm 3.93701 cal
250 mm 9.84252 cal
500 mm 19.685 cal
1000 mm 39.3701 cal
2500 mm 98.4252 cal
5000 mm 196.85 cal
10000 mm 393.701 cal
25000 mm 984.252 cal
50000 mm 1968.5 cal
100000 mm 3937.01 cal
250000 mm 9842.52 cal
500000 mm 19685 cal
1000000 mm 39370.1 cal
2500000 mm 98425.2 cal
5000000 mm 196850 cal
10000000 mm 393701 cal

Definition of Caliber

Definition
Firearms unit equal to 1/100 inch, used for bullet diameter and bore specifications.
Exact factor
1 caliber = 0.01 in = 0.254 mm
Sources
NIST SP 811

Definition of Millimeter

Definition
Metric unit equal to one thousandth (1/1000) of a meter.
Exact factor
1 mm = 0.001 m = 0.1 cm
Sources
BIPM — SI Brochure

About the Caliber

Facts & Uses

  • Firearms specifications: bullet diameter (.22 cal, .45 cal), barrel bore measurements, and ammunition standardization.
  • Military applications: artillery shell sizing, ballistics calculations, and weapon system classifications.
  • Precision manufacturing: wire gauge measurements, mechanical tolerances, and small-scale industrial applications.
  • International standards: ammunition compatibility, firearms regulations, and sporting competitions.

Curiosities

  • Exact definition: 1 caliber = 0.01 inch = 0.254 mm; provides fine gradation for small measurements.
  • Naming confusion: .22 caliber ≈ 5.6mm, but marketing names don't always match exact measurements.
  • Historical persistence: metric countries still use caliber for firearms despite otherwise adopting SI units.
  • Dual measurements: modern ammunition often shows both caliber (.308) and metric (7.62mm) designations.

Sources

About the Millimeter

Facts & Uses

  • Precision manufacturing: machining tolerances (±0.1 mm), 3D printing layer heights, and quality control specifications.
  • Medical applications: tumor measurements, surgical planning, medical device dimensions, and imaging calibration.
  • Weather measurement: rainfall accumulation (mm/day), snowfall depth; photography: lens focal lengths (50mm, 85mm).
  • Electronics: component specifications, PCB trace widths, connector dimensions; automotive: engine displacement (2000cc = 2L).

Curiosities

  • Thickness references: credit card (~0.8 mm), paper (~0.1 mm), human hair (~0.05-0.1 mm).
  • Conversion: 25.4 mm = 1 inch exactly; critical for international technical standards and manufacturing.
  • Rainfall measurement: 1 mm of rain = 1 liter per square meter, simplifying water resource calculations.
  • Camera lens focal length determines field of view: 50mm ≈ human eye perspective; 85mm = portrait lens.

Sources

Frequently Asked Questions

How many millimeters are in one caliber?

One caliber equals 25.4 millimeters. To convert, multiply the caliber value by 25.4. For the reverse, divide the millimeter value by 25.4 (or multiply by 0.0393701).

What is 0.08 calibers in millimeters?

0.08 calibers = 2.032 millimeters. This is one of the most commonly searched conversions for this pair.

Is the caliber-to-millimeter conversion exact?

Yes. The factor 25.4 is exact by international definition, not an approximation. Any imprecision comes only from the original measurement, not the conversion.

Looking for the reverse? Convert Millimeter to Caliber

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Conversion factors verified against NIST, BIPM, ISO 80000-3 1 inch = 2.54 cm by international agreement (1959). Last reviewed: March 2026
Adilson Fernandes By Adilson Fernandes
Tiago Fernandes Reviewed by Tiago Fernandes

All unit conversions on CoolConversion use conversion factors defined or documented by internationally recognised standards bodies (such as ISO and NIST), including both SI and non-SI units.