mm to Inches Conversion: Millimeters to Fractional Inches Chart
Enter a millimeter value below for an instant decimal and fractional inch result.
mm → Inches (decimal & fractional)
Direct Answer: 1mm to Inches
1mm equals 0.03937 inches. To convert any millimeter value to inches, divide it by 25.4, the exact number of millimeters in one inch. For example, 12mm ÷ 25.4 = 0.4724 inches. That decimal result rarely lands on a clean fraction, which is why this page also converts every result to the nearest common fractional inch, the format socket and wrench sizes actually use.
Millimeter to inch conversion matters most in tool and fastener contexts: matching a metric bolt to the nearest SAE socket, reading a metric dimension off a European part drawing, or checking whether a metric drill bit will pass through an SAE-dimensioned clearance hole. This page covers the full 1mm to 100mm table, the socket-relevant sizes mechanics look up most, and the length unit history behind the exact 25.4mm figure.
Full Conversion Table (1mm to 100mm)
| mm | Decimal Inches | Nearest Fraction |
|---|---|---|
| 1mm | 0.0394" | 3/64" |
| 2mm | 0.0787" | 5/64" |
| 3mm | 0.1181" | 1/8" |
| 4mm | 0.1575" | 5/32" |
| 5mm | 0.1969" | 13/64" |
| 6mm | 0.2362" | 15/64" |
| 7mm | 0.2756" | 9/32" |
| 8mm | 0.3150" | 5/16" |
| 9mm | 0.3543" | 23/64" |
| 10mm | 0.3937" | 25/64" |
| 11mm | 0.4331" | 7/16" |
| 12mm | 0.4724" | 15/32" |
| 13mm | 0.5118" | 33/64" |
| 14mm | 0.5512" | 35/64" |
| 15mm | 0.5906" | 19/32" |
| 16mm | 0.6299" | 5/8" |
| 17mm | 0.6693" | 43/64" |
| 18mm | 0.7087" | 45/64" |
| 19mm | 0.7480" | 3/4" |
| 20mm | 0.7874" | 25/32" |
| 21mm | 0.8268" | 53/64" |
| 22mm | 0.8661" | 55/64" |
| 23mm | 0.9055" | 29/32" |
| 24mm | 0.9449" | 15/16" |
| 25mm | 0.9843" | 63/64" |
| 26mm | 1.0236" | 1-1/32" |
| 27mm | 1.0630" | 1-1/16" |
| 28mm | 1.1024" | 1-7/64" |
| 29mm | 1.1417" | 1-9/64" |
| 30mm | 1.1811" | 1-3/16" |
| 31mm | 1.2205" | 1-7/32" |
| 32mm | 1.2598" | 1-17/64" |
| 33mm | 1.2992" | 1-19/64" |
| 34mm | 1.3386" | 1-11/32" |
| 35mm | 1.3780" | 1-3/8" |
| 36mm | 1.4173" | 1-27/64" |
| 37mm | 1.4567" | 1-29/64" |
| 38mm | 1.4961" | 1-1/2" |
| 39mm | 1.5354" | 1-17/32" |
| 40mm | 1.5748" | 1-37/64" |
| 41mm | 1.6142" | 1-39/64" |
| 42mm | 1.6535" | 1-21/32" |
| 43mm | 1.6929" | 1-11/16" |
| 44mm | 1.7323" | 1-47/64" |
| 45mm | 1.7717" | 1-49/64" |
| 46mm | 1.8110" | 1-13/16" |
| 47mm | 1.8504" | 1-27/32" |
| 48mm | 1.8898" | 1-57/64" |
| 49mm | 1.9291" | 1-59/64" |
| 50mm | 1.9685" | 1-31/32" |
| 51mm | 2.0079" | 2-1/64" |
| 52mm | 2.0472" | 2-3/64" |
| 53mm | 2.0866" | 2-3/32" |
| 54mm | 2.1260" | 2-1/8" |
| 55mm | 2.1654" | 2-11/64" |
| 56mm | 2.2047" | 2-13/64" |
| 57mm | 2.2441" | 2-1/4" |
| 58mm | 2.2835" | 2-9/32" |
| 59mm | 2.3228" | 2-21/64" |
| 60mm | 2.3622" | 2-23/64" |
| 61mm | 2.4016" | 2-13/32" |
| 62mm | 2.4409" | 2-7/16" |
| 63mm | 2.4803" | 2-31/64" |
| 64mm | 2.5197" | 2-33/64" |
| 65mm | 2.5591" | 2-9/16" |
| 66mm | 2.5984" | 2-19/32" |
| 67mm | 2.6378" | 2-41/64" |
| 68mm | 2.6772" | 2-43/64" |
| 69mm | 2.7165" | 2-23/32" |
| 70mm | 2.7559" | 2-3/4" |
| 71mm | 2.7953" | 2-51/64" |
| 72mm | 2.8346" | 2-53/64" |
| 73mm | 2.8740" | 2-7/8" |
| 74mm | 2.9134" | 2-29/32" |
| 75mm | 2.9528" | 2-61/64" |
| 76mm | 2.9921" | 2-63/64" |
| 77mm | 3.0315" | 3-1/32" |
| 78mm | 3.0709" | 3-5/64" |
| 79mm | 3.1102" | 3-7/64" |
| 80mm | 3.1496" | 3-5/32" |
| 81mm | 3.1890" | 3-3/16" |
| 82mm | 3.2283" | 3-15/64" |
| 83mm | 3.2677" | 3-17/64" |
| 84mm | 3.3071" | 3-5/16" |
| 85mm | 3.3465" | 3-11/32" |
| 86mm | 3.3858" | 3-25/64" |
| 87mm | 3.4252" | 3-27/64" |
| 88mm | 3.4646" | 3-15/32" |
| 89mm | 3.5039" | 3-1/2" |
| 90mm | 3.5433" | 3-35/64" |
| 91mm | 3.5827" | 3-37/64" |
| 92mm | 3.6220" | 3-5/8" |
| 93mm | 3.6614" | 3-21/32" |
| 94mm | 3.7008" | 3-45/64" |
| 95mm | 3.7402" | 3-47/64" |
| 96mm | 3.7795" | 3-25/32" |
| 97mm | 3.8189" | 3-13/16" |
| 98mm | 3.8583" | 3-55/64" |
| 99mm | 3.8976" | 3-57/64" |
| 100mm | 3.9370" | 3-15/16" |
Socket-Relevant Sizes
These are the metric sizes mechanics convert most often when reaching for a socket or wrench.
- 8mm = 0.3150" ≈ 5/16"
- 10mm = 0.3937" ≈ 25/64"
- 12mm = 0.4724" ≈ 15/32"
- 13mm = 0.5118" ≈ 33/64"
- 14mm = 0.5512" ≈ 35/64"
- 17mm = 0.6693" ≈ 43/64"
- 18mm = 0.7087" ≈ 45/64"
- 19mm = 0.7480" ≈ 3/4"
- 22mm = 0.8661" ≈ 55/64"
- 24mm = 0.9449" ≈ 15/16"
- 30mm = 1.1811" ≈ 1-3/16"
For the interchangeability rating behind each of these pairings, see the full socket conversion chart.
Common Size Lookups
- 12mm to inches: 0.4724" ≈ 15/32"
- 18mm to inches: 0.7087" ≈ 45/64"
- 30mm to inches: 1.1811" ≈ 1-3/16"
- 5/8" to mm: 0.625 × 25.4 = 15.875mm. Closest metric size is 16mm.
Why Fractional Rounding Rarely Lands on a Clean Number
A millimeter measurement divides in round base-ten steps: 1mm, 0.1mm, 0.01mm. A fractional inch divides in halves, quarters, eighths, and further powers of two: 1/2, 1/4, 1/8, down to 1/64 inch in most machinist tables. Multiplying a millimeter value by 0.03937 to reach inches, or dividing a fraction's decimal by 25.4 to reach millimeters, produces numbers from two unrelated number systems, so a clean match is the exception rather than the rule. This is exactly why a rounded reference table, not a mental shortcut, is the reliable way to move between the two.
Length Units Reference
1 inch equals exactly 25.4mm. 1mm equals 0.0394 inch. The international inch was standardized at precisely 25.4mm in 1959 by agreement among the United States, United Kingdom, Canada, Australia, and other countries. Before that agreement, the British and US inches differed by about two millionths of an inch, a gap too small to matter for hand tools but large enough to matter in precision manufacturing and metrology.
mm to Inches FAQ
What is 12mm in inches?
12mm equals 0.4724 inches, which rounds to the nearest 1/32 inch fraction of 15/32 inch. As a socket size, 12mm is closest to a 15/32 inch or 1/2 inch SAE socket depending on the tolerance needed.
What is 18mm in inches?
18mm equals 0.7087 inches, closest to 45/64 inch as an exact fraction, or 11/16 inch as the nearest common tool size, a difference of about 0.021 inch.
What is 30mm in inches?
30mm equals 1.1811 inches, closest to 1-3/16 inch, a difference of only 0.006 inch, making the two sizes a close match for most uses.
How many inches is 5/8 in mm?
5/8 inch equals 15.875mm. The closest whole metric socket size is 16mm, a difference of 0.125mm.
Is 1mm exactly 0.04 inches?
No, not exactly, though it's a close rounding. 1mm equals precisely 0.03937 inches. Rounding to 0.04 inches introduces a small error that adds up across larger measurements, so the exact 0.03937 figure matters for precision work.
Why do mm to inch conversions rarely land on a clean fraction?
Millimeters and inches are unrelated base units. A millimeter divides in round base-ten steps, while a fractional inch divides in halves, quarters, and other powers of two. Multiplying most millimeter values by 0.03937 produces a repeating or irregular decimal that only occasionally lines up with a clean sixteenth, thirty-second, or sixty-fourth of an inch.