Magnet Size Chart: Inches, Fractions and Millimeters
1 inch is exactly 25.4 mm, so 1/16 in ≈ 1.6 mm, 1/8 in ≈ 3.2 mm, 1/4 in ≈ 6.4 mm and 1/2 in = 12.7 mm. Disc sizes are listed as diameter × thickness, blocks as length × width × thickness (thickness is the magnetized direction), and rings as outer diameter × inner diameter × thickness.
Fraction, Decimal and Millimeter Chart
| Fraction (in) | Decimal (in) | Millimeters |
|---|---|---|
| 1/32 | 0.031 | 0.79 |
| 1/16 | 0.063 | 1.59 |
| 3/32 | 0.094 | 2.38 |
| 1/10 | 0.100 | 2.54 |
| 1/8 | 0.125 | 3.18 |
| 3/16 | 0.188 | 4.76 |
| 1/5 (2/10) | 0.200 | 5.08 |
| 1/4 | 0.250 | 6.35 |
| 5/16 | 0.313 | 7.94 |
| 3/8 | 0.375 | 9.53 |
| 7/16 | 0.438 | 11.11 |
| 1/2 | 0.500 | 12.70 |
| 9/16 | 0.563 | 14.29 |
| 5/8 | 0.625 | 15.88 |
| 3/4 | 0.750 | 19.05 |
| 7/8 | 0.875 | 22.23 |
| 1 | 1.000 | 25.40 |
| 1 1/8 | 1.125 | 28.58 |
| 1 1/4 | 1.250 | 31.75 |
| 1 1/2 | 1.500 | 38.10 |
| 2 | 2.000 | 50.80 |
Metric Magnets We Stock
Many projects, such as Gridfinity bins, tabletop bases and imported hardware, are designed in millimeters. A 1/4 Inch magnet (6.35 mm) won’t fit a 6 mm hole, so buy the size the design calls for.
| Metric size | In inches | Pull force |
|---|---|---|
| 3 × 1 mm Disc, N52 | 0.118 × 0.039 | 0.3 lb |
| 3 × 3 mm Cylinder, N42 | 0.118 × 0.118 | 0.6 lb |
| 4 × 2 mm Disc, N52 | 0.157 × 0.079 | 0.9 lb |
| 5 × 1 mm Disc, N52 | 0.197 × 0.039 | 0.6 lb |
| 5 × 2 mm Disc, N52 | 0.197 × 0.079 | 1.3 lb |
| 6 × 1 mm Disc, N52 | 0.236 × 0.039 | 0.8 lb |
| 6 × 2 mm Disc, N52 | 0.236 × 0.079 | 1.6 lb |
| 6 × 3 mm Disc, N42 | 0.236 × 0.118 | 2.0 lb |
| 7 × 2 mm Disc, N42 | 0.276 × 0.079 | 1.6 lb |
| 8 × 1 mm Disc, N52 | 0.315 × 0.039 | 1.2 lb |
| 8 × 2 mm Disc, N52 | 0.315 × 0.079 | 2.4 lb |
| 9 × 4.5 mm Disc, N52 | 0.354 × 0.177 | 6.4 lb |
| 10 × 1 mm Disc, N52 | 0.394 × 0.039 | 1.6 lb |
| 10 × 2 mm Disc, N52 | 0.394 × 0.079 | 3.3 lb |
| 12 × 2 mm Disc, N42 | 0.472 × 0.079 | 3.4 lb |
| 12 × 3 mm Disc, N52 | 0.472 × 0.118 | 6.8 lb |
| 21 × 7 mm Disc, N52 | 0.827 × 0.276 | 28.3 lb |
| 60 × 15 × 10 mm Bar, N52 | 2.36 × 0.59 × 0.39 | 66.5 lb |
How to Measure a Magnet
- Use calipers if you can. A ruler is fine for large magnets, but small sizes differ by fractions of a millimeter.
- Measure across the flat faces for thickness on discs, and along the magnetized direction for blocks. If you don’t know which way a block is magnetized, see what “magnetized through thickness” means.
- For rings, measure the hole too. Rings are listed outer diameter × inner diameter × thickness. Countersunk magnets also list the screw size they take.
- Compare with the product title. Our titles always list the size in the order shown above. See how our magnets are listed.
Leave Room for a Snug Fit
Plating and normal manufacturing tolerance can make a magnet a few thousandths of an inch over its nominal size. In wood, a drill bit the same size as the magnet usually gives a snug fit; for a glued fit, go about 1/64 in (0.4 mm) larger. In 3D prints, add 0.1 to 0.3 mm (see embedding magnets in 3D prints).