MM Sockets vs Standard Size (Conversion Chart)

Sockets are available in metric and standard sizes, but what if you need to switch between the two measurement systems? Why is one socket too small while the next is too loose? Argh!

Standard sockets are measured in inches, while metric sockets are measured in millimeters (mm). Depending on the region you live, one measurement system will be more common than the other. This can be frustrating when manufacturers embrace different measurement systems.

Standard sockets that work with Metric bolts (chart)

Sockets don’t fit perfectly over fasteners of the opposite measurement system, these charts can help. This socket conversion chart tells you which standard(SAE) socket to use with your metric (mm) fasteners, it is not a measurement conversion chart. (For Metric Sockets scroll to the next chart.)

  • 4 mm = use a 3/16″ socket
  • 5 mm = use a 1/4″ socket
  • 6 mm = use a 1/4″ socket
  • 7 mm = use a 5/16″ socket
  • 8 mm = use a 3/8″ socket
  • 9 mm = use a 3/8″ socket
  • 10 mm = use a 7/16″ socket
  • 11 mm = use a 7/16″ socket
  • 12 mm = use a 1/2″ socket
  • 13 mm = use a 9/16″ socket
  • 14 mm = use a 9/16″ socket
  • 15 mm = use a 5/8″ socket
  • 16 mm = use an 11/16″ socket
  • 17 mm = use an 11/16″ socket
  • 18 mm = use a 3/4″ socket
  • 19 mm = use a 3/4″ socket
  • 20 mm = use a 13/16″ socket
  • 21 mm = use a 7/8″ socket
  • 22 mm = use a 7/8″ socket
  • 23 mm = use a 15/16″ socket
  • 24 mm = use a 1″ socket
  • 25 mm = use a 1″ socket
  • 26 mm = use a 1 1/16″ socket
  • 27 mm = use a 1 1/8″ socket
  • 28 mm = use a 1 1/8″ socket
  • 29 mm = use a 1 1/4″ socket
  • 30 mm = use a 1 1/4″ socket
  • 31 mm = use a 1 1/4″ socket
  • 32 mm = use a 1 5/16″ socket
  • 33 mm = use a 1 5/16″ socket
  • 34 mm = use a 1 3/8″ socket
  • 35 mm = use a 1 7/16″ socket
  • 36 mm = use a 1 7/16″ socket
  • 37 mm = use a 1 1/2″ socket
  • 38 mm = use a 1 1/2″ socket
  • 39 mm = use a 1 9/16″ socket
  • 40 mm = use a 1 5/8″ socket
  • 41 mm = use a 1 5/8″ socket
  • 42 mm = use a 1 11/16″ socket
  • 43 mm = use a 1 3/4″ socket
  • 44 mm = use a 1 3/4″ socket
  • 45 mm = use a 1 13/16″ socket
  • 46 mm = use a 1 13/16″ socket
  • 47 mm = use a 1 7/8″ socket
  • 48 mm = use a 1 15/16″ socket
  • 49 mm = use a 1 15/16″ socket
  • 50 mm = use a 2″ socket

Metric sockets that work on Standard bolts (chart)

This socket conversion chart tells you which metric(mm) socket to use with your standard(SAE) fasteners.

  • 1/8″ = use a 4 mm socket
  • 3/16″ = use a 5 mm socket
  • 1/4″ = use a 7 mm socket
  • 5/16″ = use an 8 mm socket
  • 3/8″ = use a 10 mm socket
  • 7/16″ = use a 12 mm socket
  • 1/2″ = use a 13 mm socket
  • 9/16″ = use a 15 mm socket
  • 5/8″ = use a 16 mm socket
  • 11/16″ = use an 18 mm socket
  • 3/4″ = use a 20 mm socket
  • 13/16″ = use a 21 mm socket
  • 7/8″ = use a 23 mm socket
  • 15/16″ = use a 24 mm socket
  • 1″ = use a 26 mm socket
  • 1 1/8″ = use a 29 mm socket
  • 1 3/16″ = use a 31 mm socket
  • 1 1/4″ = use a 32 mm socket
  • 1 5/16″ = use a 34 mm socket
  • 1 3/8″ = use a 35 mm socket
  • 1 7/16″ = use a 37 mm socket
  • 1 1/2″ = use a 39 mm socket
  • 1 9/16″ = use a 40 mm socket
  • 1 5/8″ = use a 42 mm socket
  • 1 11/16″ = use a 43 mm socket
  • 1 3/4″ = use a 45 mm socket
  • 1 13/16″ = use a 47 mm socket
  • 1 7/8″ = use a 48 mm socket
  • 1 15/16″ = use a 50 mm socket
  • 2″ = use a 51 mm socket
  • 2 1/8″ = use a 54 mm socket
  • 2 3/16″ = use a 56 mm socket
  • 2 1/4″ = use a 58 mm socket
  • 2 5/16″ = use a 59 mm socket
  • 2 3/8″ = use a 61 mm socket
  • 2 7/16″ = use a 62 mm socket
  • 2 1/2″ = use a 64 mm socket
  • 2 9/16″ = use a 66 mm socket
  • 2 5/8″ = use a 67 mm socket
  • 2 11/16″ = use a 69 mm socket
  • 2 3/4″ = use a 70 mm socket
  • 2 13/16″ = use a 72 mm socket
  • 2 7/8″ = use a 74 mm socket
  • 2 15/16″ = use a 75 mm socket

Tip: If your slightly over-sized socket doesn’t fit, you can try placing a thin piece of cloth over the bolt before pressing the socket into place. The cloth will fill the small amount of extra space and allow the socket to grip the bolt more tightly.

Because there is no exact match between a bolt of one measurement system and a socket of the opposite system the charts tell you which is the CLOSEST match. If the socket is smaller than the bolt it obviously won’t fit so the closest slightly larger socket is suggested.

Example: A 33 mm metric socket is 1.29921 inches in size, which most closely matches a 1 5/16 standard size socket. A 1 5/16 standard size socket is 33.34 mm in size, which is a little bit bigger than a 33 mm socket, making it the standard size socket that best fits over a 33 mm bolt.

Unless the 33 mm nut or bolt that you need to remove is rounded, a 1 5/16th socket should work. Care should be taken not to strip the bolt, the small amount of wiggle room is sometimes enough to cause a bolt to strip. Before using a grinder or torch to loosen a stripped or rounded bolt, try padding the socket with a light cloth, it often works!

Properly organizing your sockets is key

Metric and Standard Sockets

The key to quickly grabbing the right socket when converting between metric and standard sized sockets is to keep your sockets neatly organized. Place your standard sized sockets in your toolbox from smallest to largest and place your metric sockets directly beside them.

Now, if your standard socket is slightly too big and the next smallest socket is too small, you’ll know to grab the metric socket immediately beside the standard socket for a perfect fit.

If lining up your sockets next to each other isn’t possible, you can always print a socket size conversion chart and keep it in your toolbox next to your sockets.

– Size conversion frequently asked questions. Since we’re on the topic of standard vs metric socket sizes, here are answers to the more common conversion questions

What is a 36 mm socket in standard size?

A 36 mm socket is 1 7/16″ in standard(SAE) size, almost. 1 7/16″ converts into 36.5125 mm, so a 1 7/16 socket is the standard socket that best fits a 36 mm fastener.

What is a 30 mm socket in standard size?

A 30 mm socket is 1 1/4″ in standard(SAE) size, almost. 1 1/4″ converts into 31.75 mm, so 1 1/4 is the closest standard socket that may fit your 30 mm fastener.

What is a 22 mm socket in standard size?

A 22 mm socket is 7/8″ in standard(SAE) size, almost. 7/8″ converts into 22.225 mm, so 7/8 is the closest standard socket that may fit your 22 mm fastener.

What is a 17 mm socket in inches?

A 17 mm socket is 11/16″ in standard(SAE) size, almost. 11/16″ converts into 17.4625 mm, so 11/16 is the closest standard socket that may fit your 17 mm fastener. Standard(SAE) sockets are measured in inches.

What is a 13 mm socket in SAE?

A 13 mm socket is 9/16″ in standard(SAE) size, almost. 9/16″ converts into 14.2875 mm, so 9/16 is the closest standard socket that may fit your 13 mm fastener. Note: If your 13 mm fastener is slightly worn, or you don’t have a 9/16″ socket, you may find that a 1/2″ (12.7 mm) socket works.

I hope you found these socket conversion charts helpful. Let me know!