Washer Dimensions Chart: Metric Flat Washers M1.6 to M64

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Reviewed by MLC Editorial Team | 2 October 2026

Dimensions for metric plain (flat) washers from M1.6 to M64. The normal series to ISO 7089 is the standard washer under a hex bolt or nut, and the large series to ISO 7093-1 is the wider washer used on soft materials and slotted holes. An M6 washer is 6.4 mm inside, 12 mm outside and 1.6 mm thick, an M8 washer is 8.4 mm inside, 16 mm outside and 1.6 mm thick, an M10 washer is 10.5 mm inside, 20 mm outside and 2 mm thick and an M12 washer is 13 mm inside, 24 mm outside and 2.5 mm thick.

Flat washer dimensions, normal series (ISO 7089)

Nominal dimensions. The inside diameter is the minimum hole size and the outside diameter is the maximum, so a real washer measures slightly inside those figures.

Thread size	Inside dia d1 (mm)	Outside dia d2 (mm)	Thickness h (mm)
M1.6	1.7	4	0.3
M2	2.2	5	0.3
M2.5	2.7	6	0.5
M3	3.2	7	0.5
M3.5	3.7	8	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
M14	15	28	2.5
M16	17	30	3
M18	19	34	3
M20	21	37	3
M22	23	39	3
M24	25	44	4
M27	28	50	4
M30	31	56	4
M33	34	60	5
M36	37	66	5
M39	42	72	6
M42	45	78	8
M45	48	85	8
M48	52	92	8
M52	56	98	8
M56	62	105	10
M60	66	110	10
M64	70	115	10

Large series washers (ISO 7093-1)

The large series has roughly three times the bolt diameter as its outside diameter, which spreads the load over a wider area. It covers M3 to M36. An M8 large washer is 8.4 mm inside, 24 mm outside and 2 mm thick, against 16 mm outside diameter for the normal series.

Thread size	Inside dia d1 (mm)	Outside dia d2 (mm)	Thickness h (mm)
M3	3.2	9	0.8
M3.5	3.7	11	0.8
M4	4.3	12	1
M5	5.3	15	1
M6	6.4	18	1.6
M8	8.4	24	2
M10	10.5	30	2.5
M12	13	37	3
M14	15	44	3
M16	17	50	3
M18	19	56	4
M20	21	60	4
M22	23	66	5
M24	25	72	5
M27	30	85	6
M30	33	92	6
M33	36	105	6
M36	39	110	8

How to read a washer size

A washer is named after the bolt it fits, not after any of its own dimensions. An M10 washer has a hole of 10.5 mm, which gives the M10 bolt half a millimetre of clearance. When you are identifying a loose washer, measure the hole and match it to the inside diameter column, then check the outside diameter to tell a normal series washer from a large one.

Choose the large series where the bolt passes through a slot or an oversize hole, or bears on timber, plastic or thin sheet.

ISO 7089, DIN 125 and BS 4320 are not identical

Older washer standards are still widely quoted and they do not match ISO 7089 on every size. Published tables disagree most above M36, where figures from the older DIN 125 and BS 4320 standards are often printed under an ISO 7089 heading. The values on this page are the ISO 7089:2000 and ISO 7093-1:2000 figures. If a washer has to match an existing drawing, check which standard the drawing calls up.

Related fastener dimensions

Bolt head and nut sizes for the same threads are on the bolt head sizes chart and the spanner size chart. Clearance holes are on the tap drill and clearance hole chart.

References

ISO 7089:2000 - Plain washers, normal series, product grade A
ISO 7093-1:2000 - Plain washers, large series, product grade A

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Frequently Asked Questions

What size is an M8 washer?

An M8 plain washer to ISO 7089 is 8.4 mm inside, 16 mm outside and 1.6 mm thick. The large series M8 washer to ISO 7093-1 is 8.4 mm inside, 24 mm outside and 2 mm thick.

What size is an M10 washer?

An M10 plain washer to ISO 7089 is 10.5 mm inside, 20 mm outside and 2 mm thick.

What is the difference between a normal and a large washer?

The hole is the same size but the large series has a much bigger outside diameter and is thicker. For M10 the normal series is 20 mm outside diameter and the large series is 30 mm.

How do I measure a washer?

Measure the hole diameter, the outside diameter and the thickness with calipers. The hole tells you the bolt size: it is slightly larger than the thread, so an M12 washer has a 13 mm hole.

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