3/8 Inch to MM
Fractional inch to millimeters
3/8 inch (3/8″)
9.525 mm
= 0.9525 cm · 1 inch = 25.4 mm exactly
💡 Commonly used for AC lines, small pipe.
Nearby fractional inches
| Fraction | mm | cm |
|---|---|---|
| 1/4″ | 6.35 mm | 0.635 cm |
| 5/16″ | 7.9375 mm | 0.7937 cm |
| 3/8″ | 9.525 mm | 0.9525 cm |
| 7/16″ | 11.1125 mm | 1.1112 cm |
| 1/2″ | 12.7 mm | 1.27 cm |
Also written as
3/8 to mm · 3/8 in mm · 3/8" in mm · 3/8 inch in mm · 3/8 inches to millimeters · 3/8 en mm · 0.375 inch to mm
All of these mean the same measurement. The double-prime mark (″) and the plain quote (") both stand for inches, and en mm is simply the French and Spanish wording of the same question.
Closest metric drill size
9.5 mm
3/8″ = 9.525 mm · difference 0.025 mm
Metric drills step in 0.5 mm, so a fractional inch size rarely lands exactly on one. A 0.025 mm gap is usually invisible in a clearance hole but changes the fit on a press fit or a tapped hole.
FAQ
How many mm is 3/8 inch?
3/8 inch equals 9.525 mm. Since one inch is defined as exactly 25.4 mm, the result is 25.4 × 3 ÷ 8.
Why is the value exact?
The international yard and pound agreement of 1959 fixed the inch at exactly 25.4 mm, so fractional inch conversions terminate rather than repeat.