Spanner Size Conversion Chart

Imperial to Metric · Closest socket sizes · Printable PDF

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Quick Converter

Imperial (inches)

Closest socket

13mm

Exact: 12.70 mm

Shop 1/2" Imperial Spanners on Amazon Shop 13mm Metric Sockets on Amazon

Imperial	Exact mm	Closest Socket
1/16"	1.59 mm	1.5 mm
5/64"	1.98 mm	2 mm
3/32"	2.38 mm	2.5 mm
7/64"	2.78 mm	3 mm
1/8"	3.18 mm	3 mm
9/64"	3.57 mm	3.5 mm
5/32"	3.97 mm	4 mm
3/16"	4.76 mm	5 mm
7/32"	5.56 mm	5.5 mm
1/4"	6.35 mm	6 mm
9/32"	7.14 mm	7 mm
5/16"	7.94 mm	8 mm
11/32"	8.73 mm	9 mm
3/8"	9.53 mm	10 mm
13/32"	10.32 mm	10 mm
7/16"	11.11 mm	11 mm
15/32"	11.91 mm	12 mm
1/2"	12.70 mm	13 mm
17/32"	13.49 mm	13 mm
9/16"	14.29 mm	14 mm
19/32"	15.08 mm	15 mm
5/8"	15.88 mm	16 mm
21/32"	16.67 mm	17 mm
11/16"	17.46 mm	17 mm
23/32"	18.26 mm	18 mm
3/4"	19.05 mm	19 mm
25/32"	19.84 mm	20 mm
13/16"	20.64 mm	21 mm
27/32"	21.43 mm	21 mm
7/8"	22.23 mm	22 mm
29/32"	23.02 mm	23 mm
15/16"	23.81 mm	24 mm
31/32"	24.61 mm	25 mm
1"	25.40 mm	25 mm
1-1/16"	26.99 mm	27 mm
1-1/8"	28.58 mm	29 mm
1-3/16"	30.16 mm	30 mm
1-1/4"	31.75 mm	32 mm
1-5/16"	33.34 mm	33 mm
1-3/8"	34.93 mm	35 mm
1-7/16"	36.51 mm	37 mm
1-1/2"	38.10 mm	38 mm
1-9/16"	39.69 mm	40 mm
1-5/8"	41.28 mm	41 mm
1-11/16"	42.86 mm	43 mm
1-3/4"	44.45 mm	44 mm
1-13/16"	46.04 mm	46 mm
1-7/8"	47.63 mm	48 mm
1-15/16"	49.21 mm	50 mm
2"	50.80 mm	51 mm

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Most Common

Workshop Tips

Print the PDF

Laminate it and keep it in your toolbox lid or on the workshop wall.

Shared sockets

10 mm fits both 3/8" and 13/32" — useful when a socket is close but not exact.

What is AF?

AF = Across Flats. Imperial AF sizes are the distance between the flat faces of a bolt head — what the spanner grips.

Imperial to Metric Spanner Conversion — UK Workshop Reference

Working on older machinery or equipment with imperial fasteners? This free chart converts every common imperial spanner size (1/16" to 2") to its exact metric equivalent and nearest available socket size.

Why do I need both sizes?

UK farm machinery spans decades of manufacture. Pre-1970s equipment uses Whitworth and imperial AF fasteners, while modern machines are fully metric. Knowing the crossover saves time and prevents stripped heads.

Most useful conversions on the farm

1/2" — 13 mm · extremely common on older implements
9/16" — 14 mm · hydraulic fittings and linkage pins
3/4" — 19 mm · axle nuts and drawbar bolts
7/8" — 22 mm · PTO guard bolts and wheel studs

Frequently Asked Questions

What metric socket fits a 1/2" bolt?: A 13 mm socket is the closest metric equivalent for a 1/2" (12.70 mm) imperial fastener.
Is 19 mm the same as 3/4"?: 3/4" is exactly 19.05 mm — a 19 mm socket is a near-perfect fit.
What is AF sizing?: AF = Across Flats. Imperial AF sizes specify the distance between opposite flat faces of a bolt head, which is what spanners grip.