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):

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.

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.

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%).

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.

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