Most of our neodymium magnets are made in metric sizes. If your drawing or old part is in inches, use this chart to convert the size and find the nearest magnet we stock. One inch is exactly 25.4 mm.
A metric magnet is not the same as an imperial one. A 12 x 3 mm disc is not a 1/2 x 1/8 in disc (12.7 x 3.18 mm): it is 0.7 mm smaller across and 0.18 mm thinner. That's fine for most projects, but check the fit if the magnet goes into a drilled hole or a 3D-printed pocket. Where we stock the exact imperial size, the chart says so.
Fractions of an inch in mm
| Inch (fraction) | Inch (decimal) | Millimeters |
|---|---|---|
| 1/32 in | 0.0312 in | 0.79 mm |
| 1/16 in | 0.0625 in | 1.59 mm |
| 3/32 in | 0.0938 in | 2.38 mm |
| 1/8 in | 0.125 in | 3.17 mm |
| 5/32 in | 0.1562 in | 3.97 mm |
| 3/16 in | 0.1875 in | 4.76 mm |
| 1/4 in | 0.25 in | 6.35 mm |
| 5/16 in | 0.3125 in | 7.94 mm |
| 3/8 in | 0.375 in | 9.52 mm |
| 7/16 in | 0.4375 in | 11.11 mm |
| 1/2 in | 0.5 in | 12.70 mm |
| 5/8 in | 0.625 in | 15.88 mm |
| 3/4 in | 0.75 in | 19.05 mm |
| 7/8 in | 0.875 in | 22.22 mm |
| 1 in | 1 in | 25.40 mm |
| 1-1/4 in | 1.25 in | 31.75 mm |
| 1-1/2 in | 1.5 in | 38.10 mm |
| 2 in | 2 in | 50.80 mm |
Common metric sizes in inches
| mm | Inches (decimal) | Closest common fraction (not the same size) |
|---|---|---|
| 1 mm | 0.039 in | 1/32 in = 0.79 mm, so 1 mm is 0.21 mm bigger |
| 1.5 mm | 0.059 in | 1/16 in = 1.59 mm, so 1.5 mm is 0.09 mm smaller |
| 2 mm | 0.079 in | 3/32 in = 2.38 mm, so 2 mm is 0.38 mm smaller |
| 3 mm | 0.118 in | 1/8 in = 3.17 mm, so 3 mm is 0.17 mm smaller |
| 4 mm | 0.157 in | 5/32 in = 3.97 mm, so 4 mm is 0.03 mm bigger |
| 5 mm | 0.197 in | 3/16 in = 4.76 mm, so 5 mm is 0.24 mm bigger |
| 6 mm | 0.236 in | 1/4 in = 6.35 mm, so 6 mm is 0.35 mm smaller |
| 8 mm | 0.315 in | 5/16 in = 7.94 mm, so 8 mm is 0.06 mm bigger |
| 10 mm | 0.394 in | 3/8 in = 9.52 mm, so 10 mm is 0.48 mm bigger |
| 12 mm | 0.472 in | 1/2 in = 12.70 mm, so 12 mm is 0.70 mm smaller |
| 15 mm | 0.591 in | 5/8 in = 15.88 mm, so 15 mm is 0.88 mm smaller |
| 20 mm | 0.787 in | 3/4 in = 19.05 mm, so 20 mm is 0.95 mm bigger |
| 25 mm | 0.984 in | 1 in = 25.40 mm, so 25 mm is 0.40 mm smaller |
| 30 mm | 1.181 in | 1-1/4 in = 31.75 mm, so 30 mm is 1.75 mm smaller |
| 40 mm | 1.575 in | 1-1/2 in = 38.10 mm, so 40 mm is 1.90 mm bigger |
| 50 mm | 1.969 in | 2 in = 50.80 mm, so 50 mm is 0.80 mm smaller |
| 60 mm | 2.362 in | 2-1/2 in = 63.50 mm, so 60 mm is 3.50 mm smaller |
| 80 mm | 3.150 in | 3 in = 76.20 mm, so 80 mm is 3.80 mm bigger |
| 100 mm | 3.937 in | 4 in = 101.60 mm, so 100 mm is 1.60 mm smaller |
Popular US magnet sizes and our nearest magnet
The difference column shows how much bigger (+) or smaller (−) our magnet is, per dimension, in mm.
| Shape | US size | Our nearest magnet | Difference |
|---|---|---|---|
| disc | 1/8 x 1/16 in (3.17 x 1.59 mm) | Neodymium Disc Magnet 3 x 1.5 mm N48, Nickel-Plated | −0.17, −0.09 mm |
| disc | 1/4 x 1/16 in (6.35 x 1.59 mm) | Neodymium Disc Magnet 6 x 1.5 mm N48, Nickel-Plated | −0.35, −0.09 mm |
| disc | 1/4 x 1/8 in (6.35 x 3.17 mm) | Neodymium Disc Magnet 6.5 x 3 mm N48 | +0.15, −0.17 mm |
| disc | 3/8 x 1/16 in (9.52 x 1.59 mm) | Neodymium Disc Magnet 10 x 1.5 mm | +0.48, −0.09 mm |
| disc | 3/8 x 1/8 in (9.52 x 3.17 mm) | Neodymium Disc Magnet 10 x 3 mm N48 | +0.48, −0.17 mm |
| disc | 1/2 x 1/16 in (12.7 x 1.59 mm) | Neodymium Disc Magnet 13 x 2 mm N48, Nickel-Plated | +0.30, +0.41 mm |
| disc | 1/2 x 1/8 in (12.7 x 3.17 mm) | Neodymium Disc Magnet 13 x 3 mm N48 | +0.30, −0.17 mm |
| disc | 1/2 x 1/4 in (12.7 x 6.35 mm) | Neodymium Disc Magnet 12.7 x 6.3 mm N48, Nickel-Plated | +0.00, −0.05 mm |
| disc | 3/4 x 1/8 in (19.05 x 3.17 mm) | Neodymium Disc Magnet 19 x 4 mm N48 | −0.05, +0.83 mm |
| disc | 3/4 x 1/4 in (19.05 x 6.35 mm) | Neodymium Disc Magnet 20 x 6 mm N48, Nickel-Plated | +0.95, −0.35 mm |
| disc | 1 x 1/8 in (25.4 x 3.17 mm) | Neodymium Disc Magnet 25 x 3 mm, Nickel-Plated | −0.40, −0.17 mm |
| disc | 1 x 1/4 in (25.4 x 6.35 mm) | Neodymium Disc Magnet 25 x 7 mm N48, Nickel-Plated | −0.40, +0.65 mm |
| disc | 1 x 1/2 in (25.4 x 12.7 mm) | Neodymium Disc Magnet 25 x 12 mm, Nickel-Plated | −0.40, −0.70 mm |
| cube | 1/4 in (6.35 mm) | Neodymium Cube Magnet 6 x 6 x 6 mm | −0.35 mm |
| cube | 1/2 in (12.7 mm) | Exact: Neodymium Cube Magnet 12.7 x 12.7 x 12.7 mm N48 | +0.00 mm |
| block | 1/2 x 1/4 x 1/8 in (12.7 x 6.35 x 3.17 mm) | Neodymium Block Magnet 12 x 6 x 3 mm N45 | −0.70, −0.35, −0.17 mm |
| block | 1 x 1/2 x 1/8 in (25.4 x 12.7 x 3.17 mm) | Neodymium Block Magnet 25 x 12 x 1 mm N45, Nickel-Plated | −0.40, −0.70, −2.17 mm |
| block | 1 x 1/4 x 1/8 in (25.4 x 6.35 x 3.17 mm) | Neodymium Block Magnet 25 x 6 x 2 mm N45, Nickel-Plated | −0.40, −0.35, −1.17 mm |
| block | 2 x 1/2 x 1/4 in (50.8 x 12.7 x 6.35 mm) | Neodymium Block Magnet 50 x 14 x 6 mm N45 | −0.80, +1.30, −0.35 mm |
| sphere | 1/8 in (3.17 mm) | Exact: Neodymium Sphere Magnet 3.175 mm (Magnetic Ball) | +0.00 mm |
| sphere | 1/4 in (6.35 mm) | Neodymium Sphere Magnet 6 mm (Magnetic Ball) | −0.35 mm |
| sphere | 1/2 in (12.7 mm) | Exact: Neodymium Sphere Magnet 12.7 mm (Magnetic Ball) | +0.00 mm |
| ring | 1/2 x 1/4 x 1/8 in (12.7 x 6.35 x 3.17 mm) | Neodymium Ring Magnet 12 x 7 x 3 mm N48 | −0.70, +0.65, −0.17 mm |
| rod | 1/4 x 1/2 in (6.35 x 12.7 mm) | Neodymium Rod Magnet (Cylinder) 6 x 13 mm N48, Nickel-Plated | −0.35, +0.30 mm |
| rod | 1/2 x 1/2 in (12.7 x 12.7 mm) | Neodymium Rod Magnet (Cylinder) 12 x 15 mm N48 | −0.70, +2.30 mm |
Can't find a close enough size? Request a quote: we supply custom sizes in volume, including exact imperial sizes.
Magnets we stock in exact imperial sizes
How to measure a magnet
- Disc and rod magnets: diameter x thickness (or length). A "1/2 x 1/8" disc is 1/2 in across and 1/8 in thick.
- Block magnets: length x width x thickness. On our block magnets the last dimension is the direction of magnetization.
- Ring magnets: outer diameter x inner diameter x thickness.
- Exact dimensions: sizes in titles are nominal. Check the dimensions on each product page.
FAQ
Is a 12 mm magnet the same as a 1/2 inch magnet?
No. 1/2 in is 12.7 mm, so a 12 mm magnet is 0.7 mm (about 0.03 in) smaller. For a 1/2 in hole, choose a 12 or 13 mm magnet depending on whether it must fit inside or cover it.
Why are your sizes in mm?
Our magnets are made to metric sizes. We show inches next to mm so you can compare.
Can I order exact imperial sizes?
Yes. The sizes in the table above are stocked. Other imperial sizes are available as custom orders in volume: bulk and custom orders.
Ordering in the US? See US shipping: free from $50.