Workshop & Hardware
What Size Is This Washer?
Compare the hole and the outside edge to actual-size circles. Useful when washers are unmarked or mixed in a hardware drawer.
Confirm calibration
Calibrate your display for best accuracy before comparing objects.
Compare this washer
Avoid pressing sharp metal against the display. Hold the washer just above the reference circles. Washer standards vary — results list possible candidates, not a single guaranteed part number.
1. Inner diameter (hole)
2. Outer diameter
Place washer over nested circles
Can't find what you're measuring?
Inner vs outer diameter
The inner diameter is the hole. It is usually a little larger than the bolt it fits (for example, an M5 ISO washer hole is 5.3 mm, not 5.0 mm).
The outer diameter varies by series. ISO normal-series, large-series, and ASME Type A narrow/wide washers are not interchangeable by name alone.
When two standards look similar, this tool lists multiple candidates with measured differences instead of forcing one answer.
ISO 7089 washer chart
Normal series plain washers. Other ISO series have different outer diameters.
| For bolt | Inner (mm) | Outer (mm) | Thickness (mm) |
|---|---|---|---|
| M2 | 2.2 | 5 | 0.3 |
| M2.5 | 2.7 | 6 | 0.5 |
| M3 | 3.2 | 7 | 0.5 |
| M4 | 4.3 | 9 | 0.8 |
| M5 | 5.3 | 10 | 1 |
| M6 | 6.4 | 12 | 1.6 |
| M8 | 8.4 | 16 | 1.6 |
| M10 | 10.5 | 20 | 2 |
| M12 | 13 | 24 | 2.5 |
| M16 | 17 | 30 | 3 |
| M20 | 21 | 37 | 3 |
Source: ISO 7089 plain washers (normal series / DIN 125 Form A).
ASME Type A washer chart
| Washer | For | Inner (mm) | Outer (mm) |
|---|---|---|---|
| #6 Type A | #6 | 3.96 | 9.53 |
| #8 Type A | #8 | 4.78 | 11.13 |
| #10 Type A | #10 | 5.56 | 12.70 |
| 1/4" Type A narrow | 1/4" | 7.14 | 15.88 |
| 1/4" Type A wide | 1/4" | 7.92 | 18.64 |
| 5/16" Type A narrow | 5/16" | 8.74 | 17.48 |
| 5/16" Type A wide | 5/16" | 9.53 | 22.23 |
| 3/8" Type A narrow | 3/8" | 10.31 | 20.62 |
| 3/8" Type A wide | 3/8" | 11.13 | 25.40 |
| 1/2" Type A narrow | 1/2" | 13.49 | 26.97 |
| 1/2" Type A wide | 1/2" | 14.27 | 34.92 |
Source: ASME B18.21.1 Type A plain washers (preferred sizes). Closest standard size. Calibrate for best accuracy.
Common questions
How do I identify an unmarked washer?
Calibrate your screen and compare both the hole (inner diameter) and the outside edge (outer diameter) to actual-size circles from ISO 7089 and ASME Type A charts. Matching only one dimension is often ambiguous.
What is the difference between washer ID and OD?
ID is the hole (inner diameter). OD is the outside edge (outer diameter). Both are needed to identify a washer series. Thickness helps but is not enough alone.
Why is an M5 washer hole bigger than 5 mm?
Clearance. In this ISO 7089 normal-series data, an M5 washer hole (d1) is 5.3 mm with a 10 mm outer diameter—so the bolt can pass through without binding. The hole is intentionally larger than the bolt’s 5 mm major diameter.
Is washer ID the same as bolt size?
Usually not. The hole is typically a little larger than the bolt nominal size. For example an M5 ISO washer hole is 5.3 mm, not 5.0 mm.
Why might ISO and ASME washers look similar?
ISO series and ASME Type A washers are not interchangeable by name alone. When candidates overlap, this tool lists multiple matches with measured differences instead of forcing one answer.
Does thickness identify the washer alone?
Thickness helps but is not enough by itself. Inner and outer diameter together are the primary match, then series and thickness.