Imperial to Metric Conversion Table for Bearing Sizes

When you are trying to match a bearing, shaft, or bore size across two different measurement systems, small rounding errors can send you looking at the wrong part entirely. Bearings are sold in both imperial (inch) and metric (millimetre) sizing depending on the manufacturer and country of origin, and being able to move confidently between the two is one of the most useful skills for anyone sourcing replacement bearings.

This page gives you a full reference chart for converting inch measurements — shown as both a fraction and a decimal — into their millimetre equivalents. It covers everything from tiny fractional sizes right up to full inch and multi-inch measurements, so whether you are checking a 1/64" clearance or a 100" span, you will find the matching mm value below.

Why Imperial and Metric Bearings Are Not Always Interchangeable

It is tempting to assume that the closest metric bearing to an imperial size will work as a substitute, but even a fraction of a millimetre of difference in bore, outer diameter, or width can mean a bearing that is too loose, too tight, or simply will not seat correctly. Whenever you are converting a size to go shopping for a replacement bearing, always confirm the exact figure against this table rather than rounding by eye.

How to Use This Chart

Find the inch measurement you have — either as a fraction (for example 1/64") or as a decimal (for example 0.0156") — in the left-hand columns, then read across to see the equivalent size in millimetres. If you already have a metric figure and want to go the other way, scan the mm column instead and read back to the inch equivalent.

For guidance on the order bearing sizes are listed in (bore, then outside diameter, then width) see our companion guide, How to Measure Bearings.

Full Conversion Table

| Fractional (in) | Decimal (in) | Millimetres (mm) | |---|---|---| | | 0.0039 | 0.1000 | | | 0.0079 | 0.2000 | | | 0.0118 | 0.3000 | | 1/64 | 0.0156 | 0.3969 | | | 0.0157 | 0.4000 | | | 0.0197 | 0.5000 | | | 0.0236 | 0.6000 | | | 0.0276 | 0.7000 | | 1/32 | 0.0313 | 0.7938 | | | 0.0315 | 0.8000 | | | 0.0354 | 0.9000 | | | 0.0394 | 1.0000 | | | 0.0433 | 1.1000 | | 3/64 | 0.0469 | 1.1906 | | | 0.0472 | 1.2000 | | | 0.0512 | 1.3000 | | | 0.0551 | 1.4000 | | | 0.0591 | 1.5000 | | 1/16 | 0.0625 | 1.5875 | | | 0.0630 | 1.6000 | | | 0.0669 | 1.7000 | | | 0.0709 | 1.8000 | | | 0.0748 | 1.9000 | | 5/64 | 0.0781 | 1.9844 | | | 0.0787 | 2.0000 | | | 0.0827 | 2.1000 | | | 0.0866 | 2.2000 | | | 0.0906 | 2.3000 | | 3/32 | 0.0938 | 2.3813 | | | 0.0945 | 2.4000 | | | 0.0984 | 2.5000 | | 7/64 | 0.1094 | 2.7781 | | | 0.1181 | 3.0000 | | 1/8 | 0.1250 | 3.1750 | | | 0.1378 | 3.5000 | | 9/64 | 0.1406 | 3.5719 | | 5/32 | 0.1563 | 3.9688 | | | 0.1575 | 4.0000 | | 11/64 | 0.1719 | 4.3656 | | | 0.1772 | 4.5000 | | 3/16 | 0.1875 | 4.7625 | | | 0.1969 | 5.0000 | | 13/64 | 0.2031 | 5.1594 | | | 0.2165 | 5.5000 | | 7/32 | 0.2188 | 5.5563 | | 15/64 | 0.2344 | 5.9531 | | | 0.2362 | 6.0000 | | 1/4 | 0.2500 | 6.3500 | | | 0.2559 | 6.5000 | | 17/64 | 0.2656 | 6.7469 | | | 0.2756 | 7.0000 | | 9/32 | 0.2813 | 7.1438 | | | 0.2953 | 7.5000 | | 19/64 | 0.2969 | 7.5406 | | 5/16 | 0.3125 | 7.9375 | | | 0.3150 | 8.0000 | | 21/64 | 0.3281 | 8.3344 | | | 0.3346 | 8.5000 | | 11/32 | 0.3438 | 8.7313 | | | 0.3543 | 9.0000 | | 23/64 | 0.3594 | 9.1281 | | | 0.3740 | 9.5000 | | 3/8 | 0.3750 | 9.5250 | | 25/64 | 0.3906 | 9.9219 | | | 0.3937 | 10.0000 | | 13/32 | 0.4063 | 10.3188 | | | 0.4134 | 10.5000 | | 27/64 | 0.4219 | 10.7156 | | | 0.4331 | 11.0000 | | 7/16 | 0.4375 | 11.1125 | | | 0.4528 | 11.5000 | | 29/64 | 0.4531 | 11.5094 | | 15/32 | 0.4688 | 11.9063 | | | 0.4724 | 12.0000 | | 31/64 | 0.4844 | 12.3031 | | | 0.4921 | 12.5000 | | 1/2 | 0.5000 | 12.7000 | | | 0.5118 | 13.0000 | | 33/64 | 0.5156 | 13.0969 | | 17/32 | 0.5313 | 13.4938 | | | 0.5315 | 13.5000 | | 35/64 | 0.5469 | 13.8906 | | | 0.5512 | 14.0000 | | 9/16 | 0.5625 | 14.2875 | | | 0.5709 | 14.5000 | | 37/64 | 0.5781 | 14.6844 | | | 0.5906 | 15.0000 | | 19/32 | 0.5938 | 15.0813 | | 39/64 | 0.6094 | 15.4781 | | | 0.6102 | 15.5000 | | 5/8 | 0.6250 | 15.8750 | | | 0.6299 | 16.0000 | | 41/64 | 0.6406 | 16.2719 | | | 0.6496 | 16.5000 | | 21/32 | 0.6563 | 16.6688 | | | 0.6693 | 17.0000 | | 43/64 | 0.6719 | 17.0656 | | 11/16 | 0.6875 | 17.4625 | | | 0.6890 | 17.5000 | | 45/64 | 0.7031 | 17.8594 | | | 0.7087 | 18.0000 | | 23/32 | 0.7188 | 18.2563 | | | 0.7283 | 18.5000 | | 47/64 | 0.7344 | 18.6531 | | | 0.7480 | 19.0000 | | 3/4 | 0.7500 | 19.0500 | | 49/64 | 0.7656 | 19.4469 | | | 0.7677 | 19.5000 | | 25/32 | 0.7813 | 19.8438 | | | 0.7874 | 20.0000 | | 51/64 | 0.7969 | 20.2406 | | | 0.8071 | 20.5000 | | 13/16 | 0.8125 | 20.6375 | | | 0.8268 | 21.0000 | | 53/64 | 0.8281 | 21.0344 | | 27/32 | 0.8438 | 21.4313 | | | 0.8465 | 21.5000 | | 55/64 | 0.8594 | 21.8281 | | | 0.8661 | 22.0000 | | 7/8 | 0.8750 | 22.2250 | | | 0.8858 | 22.5000 | | 57/64 | 0.89063 | 22.6219 | | | 0.9055 | 23.0000 | | 29/32 | 0.90625 | 23.0188 | | 59/64 | 0.92188 | 23.4156 | | | 0.9252 | 23.5000 | | 15/16 | 0.93750 | 23.8125 | | | 0.9449 | 24.0000 | | 61/64 | 0.95313 | 24.2094 | | | 0.9646 | 24.5000 | | 31/32 | 0.96875 | 24.6063 | | | 0.9843 | 25.0000 | | 63/64 | 0.98438 | 25.0031 | | 1 | 1.000 | 25.40 | | | 1.0039 | 25.5000 | | | 1.0236 | 26.0000 | | | 1.0433 | 26.5000 | | | 1.0630 | 27.0000 | | | 1.0827 | 27.5000 | | | 1.1024 | 28.0000 | | | 1.1220 | 28.5000 | | | 1.1417 | 29.0000 | | | 1.1614 | 29.5000 | | | 1.1811 | 30.0000 | | | 1.2205 | 31.0000 | | 1 1/4 | 1.2500 | 31.7500 | | | 1.2598 | 32.0000 | | | 1.2992 | 33.0000 | | | 1.3386 | 34.0000 | | | 1.3780 | 35.0000 | | | 1.4173 | 36.0000 | | | 1.4567 | 37.0000 | | | 1.4961 | 38.0000 | | 1 1/2 | 1.5000 | 38.1000 | | | 1.5354 | 39.0000 | | | 1.5748 | 40.0000 | | | 1.6142 | 41.0000 | | | 1.6535 | 42.0000 | | | 1.6929 | 43.0000 | | | 1.7323 | 44.0000 | | 1 3/4 | 1.7500 | 44.4500 | | | 1.7717 | 45.0000 | | | 1.8110 | 46.0000 | | | 1.8504 | 47.0000 | | | 1.8898 | 48.0000 | | | 1.9291 | 49.0000 | | | 1.9685 | 50.0000 | | 2 | 2.0000 | 50.8000 | | | 2.0079 | 51.0000 | | | 2.0472 | 52.0000 | | | 2.0866 | 53.0000 | | | 2.1260 | 54.0000 | | | 2.1654 | 55.0000 | | | 2.2047 | 56.0000 | | | 2.2441 | 57.0000 | | 2 1/4 | 2.2500 | 57.1500 | | | 2.2835 | 58.0000 | | | 2.3228 | 59.0000 | | | 2.3622 | 60.0000 | | | 2.4016 | 61.0000 | | | 2.4409 | 62.0000 | | | 2.4803 | 63.0000 | | 2 1/2 | 2.5000 | 63.5000 | | | 2.5197 | 64.0000 | | | 2.5591 | 65.0000 | | | 2.5984 | 66.0000 | | | 2.6378 | 67.0000 | | | 2.6772 | 68.0000 | | | 2.7165 | 69.0000 | | 2 3/4 | 2.7500 | 69.8500 | | | 2.7559 | 70.0000 | | | 2.7953 | 71.0000 | | | 2.8346 | 72.0000 | | | 2.8740 | 73.0000 | | | 2.9134 | 74.0000 | | | 2.9528 | 75.0000 | | | 2.9921 | 76.0000 | | 3 | 3.0000 | 76.2000 | | | 3.0315 | 77.0000 | | | 3.0709 | 78.0000 | | | 3.1102 | 79.0000 | | | 3.1496 | 80.0000 | | | 3.1890 | 81.0000 | | | 3.2283 | 82.0000 | | | 3.2677 | 83.0000 | | | 3.3071 | 84.0000 | | | 3.3465 | 85.0000 | | | 3.3858 | 86.0000 | | | 3.4252 | 87.0000 | | | 3.4646 | 88.0000 | | 3 1/2 | 3.5000 | 88.9000 | | | 3.5039 | 89.0000 | | | 3.5433 | 90.0000 | | | 3.5827 | 91.0000 | | | 3.6220 | 92.0000 | | | 3.6614 | 93.0000 | | | 3.7008 | 94.0000 | | | 3.7402 | 95.0000 | | | 3.7795 | 96.0000 | | | 3.8189 | 97.0000 | | | 3.8583 | 98.0000 | | | 3.8976 | 99.0000 | | | 3.9370 | 100.0000 | | 4 | 4.0000 | 101.6000 | | | 4.3307 | 110.0000 | | 4 1/2 | 4.5000 | 114.3000 | | | 4.7244 | 120.0000 | | 5 | 5.0000 | 127.0000 | | | 5.1181 | 130.0000 | | | 5.5118 | 140.0000 | | | 5.9055 | 150.0000 | | 6 | 6.0000 | 152.4000 | | | 6.2992 | 160.0000 | | | 6.6929 | 170.0000 | | | 7.0866 | 180.0000 | | | 7.4803 | 190.0000 | | | 7.8740 | 200.0000 | | 8 | 8.0000 | 203.2000 | | | 9.8425 | 250.0000 | | 10 | 10.0000 | 254.0000 | | 20 | 20.0000 | 508.0000 | | 30 | 30.0000 | 762.0000 | | 40 | 40.0000 | 1016.000 | | 60 | 60.0000 | 1524.000 | | 80 | 80.0000 | 2032.000 | | 100 | 100.0000 | 2540.000 |

Quick Reference Notes

Fractional inch values are shown only where they correspond to a common fraction (for example 1/64", 1/32", 1/16"); decimal-only rows fall between these common fractions.
Decimal inch values are rounded to four decimal places.
Millimetre values are the standard rounded metric equivalents used across the bearing industry.
Always double-check bore, outer diameter, and width individually — a bearing's full size code is a combination of three separate measurements, and each one needs to convert cleanly for a substitute part to fit properly.

If you are unsure which size you actually need, get in touch with our team and we will help you match the correct bearing for your application.