Metric to US Conversion Chart for Fasteners (mm to Inches & Fractions)
Metric to US Conversion Chart for Fasteners
Matching metric fasteners with US inch equivalents can be confusing. This quick-reference chart makes it easy: compare metric (mm) sizes with their decimal inch values and the closest common fraction mechanics use every day. For example, if you see a screw labeled M6, that simply means 6 mm in diameter.
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| Metric (mm) | Inches (in.) | Closest Fraction* |
|---|---|---|
| 1.5 mm | 0.059 in. | 1/16" |
| 2 mm | 0.0787 in. | 5/64" |
| 2.5 mm | 0.0984 in. | 3/32" |
| 3 mm | 0.1181 in. | 1/8" |
| 4 mm | 0.1575 in. | 5/32" |
| 5 mm | 0.1969 in. | 3/16" |
| 6 mm | 0.2362 in. | 1/4" |
| 8 mm | 0.3150 in. | 5/16" |
| 10 mm | 0.3937 in. | 13/32" |
| 12 mm | 0.4724 in. | 15/32" |
| 14 mm | 0.5512 in. | 9/16" |
| 15 mm | 0.5906 in. | 19/32" |
| 16 mm | 0.6299 in. | 5/8" |
| 18 mm | 0.7087 in. | 11/16" |
| 20 mm | 0.7874 in. | 25/32" |
| 22 mm | 0.8661 in. | 7/8" |
| 25 mm | 0.9843 in. | 1" |
| 28 mm | 1.1024 in. | 1-1/8" |
| 30 mm | 1.1811 in. | 1-3/16" |
| 35 mm | 1.3780 in. | 1-3/8" |
| 40 mm | 1.5748 in. | 1-9/16" |
| 45 mm | 1.7717 in. | 1-3/4" |
| 50 mm | 1.9685 in. | 2" (approx.) |
| 55 mm | 2.1654 in. | 2-1/8" |
| 60 mm | 2.3622 in. | 2-3/8" |
| 65 mm | 2.5591 in. | 2-9/16" |
| 70 mm | 2.7559 in. | 2-3/4" |
| 75 mm | 2.9528 in. | 2-15/16" |
| 80 mm | 3.1496 in. | 3-1/8" |
| 85 mm | 3.3465 in. | 3-5/16" |
| 90 mm | 3.5433 in. | 3-1/2" |
| 95 mm | 3.7402 in. | 3-3/4" |
| 100 mm | 3.9370 in. | 3-15/16" |
| 110 mm | 4.3307 in. | 4-5/16" |
| 120 mm | 4.7244 in. | 4-3/4" |
| 125 mm | 4.9213 in. | 5" |
| 130 mm | 5.1181 in. | 5-1/8" |
| 140 mm | 5.5118 in. | 5-1/2" |
| 150 mm | 5.9055 in. | 6" |
| 160 mm | 6.2992 in. | 6-5/16" |
| 170 mm | 6.6929 in. | 6-11/16" |
| 175 mm | 6.8898 in. | 6-7/8" |
| 180 mm | 7.0866 in. | 7-1/16" |
| 190 mm | 7.4803 in. | 7-1/2" |
| 200 mm | 7.8740 in. | 7-7/8" |
* Fractions are approximations—rounded for common tool and fastener use.
Tip: Fastener sizes are often written as M# × Length. For example, an M4 × 16 screw is 4 mm in diameter and 16 mm long.
FAQ: Metric ↔ US Conversion
Are metric and US (inch) fasteners interchangeable?
No. This chart compares dimensions only. Threads differ (pitch vs TPI), so mixing systems can damage threads and reduce strength.
What does “closest fraction” mean?
It’s the nearest common fractional inch size used in practice. It’s rounded for convenience and may not be exact.
How do I convert metric thread pitch to TPI?
You don’t one-to-one. Metric uses distance between threads (mm), US uses threads per inch. Use dedicated pitch/TPI tables for threads: Metric Pitch and US TPI.
Which page helps me identify my screw size?
Use our measuring guide and printable ruler to confirm diameter and length before ordering.
Where can I buy metric fasteners?
Right here: browse our Metric Fasteners Collection—fast shipping from Milton, Florida.