Socket set Conversion Chart

How often have you been working on a job where you need two of the same size sockets?

Instead of reaching for an adjustable spanner or an open ended wrench, how about using the metric or SAE equivalent?

A large number of socket sets have both SAE and metric sockets in the same case. But did you know that a good number of sockets are close to being the same size. In fact, they are often such a close match that cheaper sets sometimes leave out the metric equivalent.

The chart below converts SAE (inch system) wrenches to standard metric sized wrenches. So now you can pop a metric socket on the head of a bolt, and use the SAE socket on the nut end. Post this chart on your workshop wall or tool box lid to help find a close wrench fit.

It’s important to understand that the matches shown below are not always exact matches. However, they are certainly close enough to be interchanged – unless you are using a torque wrench or a breaker bar. I also wouldn’t use an equivalent size if the bolt is tight, stuck or damaged in any way.

In most cases, it is best to use 6 point sockets – the 12 point versions will cause greater slippage and may damage your bolt or nut.

The following sizes are good fits (less than 1% difference):

SAE Metric
5/32″ 4mm
5/16″ 8mm
7/16″ 11mm
15/32″ 12mm
19/32″ 15mm
5/8″ 16mm
3/4″ 19mm
25/32″ 20mm
7/8″ 22mm
29/32″ 23mm
15/16″ 24mm
1-1/16″ 27mm
1-3/16″ 30mm
1-1/4″ 32mm
1-5/16″ 33mm
1-3/8″ 35mm
1-1/2″ 38mm
1-5/8″ 41mm
1-3/4″ 44mm

 

The following sizes are sloppy fits, and extra care should be taken:

WARNING : The sockets with bigger positive differences may damage your fastener by rounding the head. The negative differences may mean the socket is too small for the fastener.

SAE Metric Difference
9/32″ 7mm +2.05%
3/8″ 10mm -4.75%
1/2″ 13mm -2.31%
9/16″ 14mm +2.05%
21/32″ 17mm +1.95%
11/16″ 17mm +2.72%
13/16″ 21mm -1.73%
1″ 25mm +1.60%
1-1/8″ 29mm -1.47%
1-7/16″ 37mm -1.32%

How to convert SAE sizes to Metric

Converting SAE socket sizes to metric measurements is fairly easy if you have a calculator at hand, or are excellent at mental arithmetic.

Most if the time you will find socket sizes are written as a fraction of an inch (eg 5/8″) This is also called an SAE or imperial measurement.

To convert SAE less than an inch to metric, we need to divide the top number by the bottom number and multiply it by 25.4

 

The reason we use 25.4 is because there are 25.4 millimeters in an inch (This figure never changes).

For example, 5/8″ is converted to metric as follows:

5 divided by 8 and multiplied by 25.4

On a calculator : 5 ÷ 8 × 25.4 = 15.875

When we look at this example, you can see that 16mm and 5/8″ are not an exact match.

But when we round the result to 16mm, they are only 0.125 of a millimeter apart. When this is expressed as a percentage difference, the result is only 0.78 of a percent (a very small amount – less than 1%).

As a rule of thumb, if the difference in the converted size is more than 1%, you need to be careful that you don’t round the head of your fasteners.

 

Larger sockets are written as 1-3/8″ or 1 3/8″

There is an extra step to convert sockets that are an inch or larger.

To convert sockets that are an inch or more, you need to ignore the first digit and divide the top number of the fraction by the bottom number. Once you have this, multiple the answer by 25.4, and then ADD on another 25.4 for the leading one inch.

 

On a calculator, 1-3/8″ is calculated as:

3 ÷ 8 × 25.4 + 25.4 = 34.925 mm (Rounds up to 35mm)

All socket sizes in order from smallest to largest

Socket
Size
1/4″
Drive
3/8″
Drive
1/2″
Drive
3/4″
Drive
1″
Drive
mm inch dec Alternate
Socket
Variation
inch dec
3mm Y 3.000 0.118
3.2mm Y 3.200 0.126
3.5mm Y 3.500 0.138
5/32″ Y 3.969 0.156 4mm -0.001
4mm Y 4.000 0.157 5/32″ 0.001
4.5mm Y 4.500 0.177
3/16″ Y 4.763 0.188
5mm Y 5.000 0.197
5.5mm Y Y 5.500 0.217
7/32″ Y Y 5.556 0.219
6mm Y Y 6.000 0.236
1/4″ Y Y 6.350 0.250
7mm Y Y 7.000 0.276
9/32″ Y Y 7.144 0.281
5/16″ Y Y 7.938 0.313 8mm -0.002
8mm Y Y Y 8.000 0.315 5/16″ 0.002
11/32″ Y Y Y 8.731 0.344
9mm Y Y Y 9.000 0.354
3/8″ Y Y Y 9.525 0.375
10mm Y Y Y 10.000 0.394
11mm Y Y Y 11.000 0.433 7/16″ -0.004
7/16″ Y Y Y 11.113 0.438 11mm 0.004
15/32″ Y Y Y 11.906 0.469 12mm -0.004
12mm Y Y Y 12.000 0.472 15/32″ 0.004
1/2″ Y Y Y 12.700 0.500
13mm Y Y Y 13.000 0.512
14mm Y Y Y 14.000 0.551
9/16″ Y Y Y 14.288 0.563
15mm Y Y Y 15.000 0.591 19/32″ -0.003
19/32″ Y 15.081 0.594 15mm 0.003
5/8″ Y Y 15.875 0.625 16mm -0.005
16mm Y Y 16.000 0.630 5/8″ 0.005
21/32″ Y 16.669 0.656
17mm Y Y 17.000 0.669
11/16″ Y Y 17.463 0.688
18mm Y Y 18.000 0.709
19mm Y Y Y 19.000 0.748 3/4″ -0.002
3/4″ Y Y Y 19.050 0.750 19mm 0.002
25/32″ Y Y 19.844 0.781 20mm -0.006
20mm Y Y Y 20.000 0.787 25/32″ 0.006
13/16″ Y Y Y 20.638 0.813
21mm Y Y Y 21.000 0.827
22mm Y Y Y 22.000 0.866 7/8″ -0.009
7/8″ Y Y 22.225 0.875 22mm 0.009
23mm Y Y 23.000 0.906 29/32″ -0.001
29/32″ Y Y 23.019 0.906 23mm 0.001
15/16″ Y Y 23.813 0.938 24mm -0.007
24mm Y Y 24.000 0.945 15/16″ 0.007
25mm Y Y 25.000 0.984
1″ Y 25.400 1.000
26mm Y Y 26.000 1.024
1-1/16″ Y Y 26.988 1.063 27mm 0.000
27mm Y Y 27.000 1.063 1-1/16″ 0.000
28mm Y Y 28.000 1.102
1-1/8″ Y Y 28.575 1.125
29mm Y Y 29.000 1.142
30mm Y Y 30.000 1.181 1-3/16″ -0.006
1-3/16″ Y Y 30.163 1.188 30mm 0.006
31mm Y 31.000 1.220
1-1/4″ Y Y 31.750 1.250 32mm -0.010
32mm Y 32.000 1.260 1-1/4″ 0.010
33mm Y 33.000 1.299 1-5/16″ -0.013
1-5/16″ Y 33.338 1.313 33mm 0.013
34mm Y 34.000 1.339
1-3/8″ Y 34.925 1.375 35mm -0.003
35mm Y 35.000 1.378 1-3/8″ 0.003
36mm Y Y 36.000 1.417
1-7/16″ Y 36.513 1.438
38mm Y Y 38.000 1.496 1-1/2″ -0.004
1-1/2″ Y Y 38.100 1.500 38mm 0.004
41mm Y Y 41.000 1.614 1-5/8″ -0.011
1-5/8″ Y Y 41.275 1.625 41mm 0.011
42mm Y 42.000 1.654
1-11/16″ Y Y 42.863 1.688
44mm Y 44.000 1.732 1-3/4″ -0.018
1-3/4″ Y Y 44.450 1.750 44mm 0.018
46mm Y 46.000 1.811 1-13/16″ -0.001
1-13/16″ Y Y 46.038 1.813 46mm 0.001
1-7/8″ Y Y 47.625 1.875
50mm Y 50.000 1.969
2″ Y Y 50.800 2.000 2-1/8″ -0.125
2-1/8″ Y Y 53.975 2.125 54mm 0.125
54mm Y 54.000 2.126
55mm Y 55.000 2.165
2-3/16″ Y Y 55.563 2.188
2-1/4″ Y Y 57.150 2.250
58mm Y 58.000 2.283
60mm Y 60.000 2.362 2-3/8″ -0.013
2-3/8″ Y 60.325 2.375 60mm 0.013
63mm Y 63.000 2.480
2-1/2″ Y 63.500 2.500
65mm Y 65.000 2.559
2-5/8″ Y 66.675 2.625
67mm Y 67.000 2.638
2-3/4″ Y 69.850 2.750
70mm Y 70.000 2.756
71mm Y 71.000 2.795
2-15/16″ Y 74.613 2.938
75mm Y 75.000 2.953
3″ Y 76.200 3.000
77mm Y 77.000 3.031
3-1/8″ Y 79.375 3.125
80mm Y 80.000 3.150