Wrench Size Chart and Different Types converted in mm, sae, …

This post was last updated on April 13th, 2023 at 08:57 pm

Wrench is the typical American term while “Spanner” is its name in British English, some people also call it a spanner wrench. Don’t be confused by the name, all the names refer to the same tool you have seen a mechanic or a plumber use (skip straight to the Common Wrench Size Chart).

There is a wide variety of bolts and nuts to work on. Wrenches are manufactured with several types of materials in various sizes. The size of the wrench is usually stamped on it. The imperial units are used in the US and are generally referred to as the SAE wrench. Their sizes are numbered in fractions of inches. Metric tools are used in several countries and their sizes in whole numbers of millimeters. 

Jump right into the Frequently Asked Questions

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Table of Content Wrench

Common Wrench Size Chart

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Common wrench sizes are determined by a measurement scale based on the common sizes of the fastener head of the various fasteners (bolt, nut, socket, screw head, etc). The wrench conversion chart below shows each common size of the wrench.

Bolt Size (SAE/US)Bolt Size (Metric/mm)Wrench Size (SAE/US)Wrench Size (Metric)

Learn more about how to choose the right size wrench (video)

Metric vs Standard, Imperial or SAE – Wrenches, Sockets, Bolt Size Chart + Mechanic Math by Hartz HomeStead

Bolt Size Conversion Chart

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Don’t be confused here; the bolt’s size will determine the wrench you use on it. However, the size of the wrench is measured by measuring its diameter, and the number you get after measuring the diameter is NOT the same as the number written on the wrench meant for that bolt (or nut). For example, a bolt with a diameter of 1/8 inches (3 mm) needs a wrench with the number 5/16 or the number 8 stamped on it.

Common sizes of the metric bolt are not identical to the common types of bolts in imperial sizes. You have to know the fitting standard of the machine you are working on to know the correct size bolt and the correct wrench size. Based on each measurement unit, the best common form is written on the opposite.

Diameter (SAE/US)Diameter (Metric/mm)

Is the size the same for all types of wrench?

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A job-specific toolbox such as a bike tool kit will have wrenches that are common sizing and have an advantage for applications relating to the machine, in this case, a bicycle. But wrench sets purchased for commercial applications such as automotive applications will be based on the standard sizing scheme. 

The methods of sizing can vary but the major wrench types based on wrench designs are divided into two groups: wrenches meant for small bolts and nuts and the larger wrenches meant for bigger fastener types such as larger size bolts, nuts, and even pipes and oil filters.

wrench size chart
Image Source: HomeStratosphere.com

Small wrenches include the combination wrench, substitute wrench, socket wrench, closed wrench, and key wrenches. Larger wrenches include the adjustable wrench, ratcheting wrench, circular wrench, and jumbo wrenches.

Standard Wrench sizes explained (video)

Standard wrench sizes made EASY by D&E In The Garage

Frequently Asked Questions

What are the standard wrench sizes?

Based on standard sizes, there are two types of wrenches. From smallest to largest, the standard wrench sizes in the US are 5/8, 19/32, 9/16, 1/2, 7/16, 3/8, 11/32, 5/16, 9/32, 1/4, 7/32, 3/16, 5/32, and 1/8. From smallest to largest, the standard metric wrench sizes are 4, 3, 8, 10, 12, 14, 16, 18, 20, 22, and 24.

How are wrench sizes measured?

The size of a wrench is measured with calipers. The distance between the two farthest points of the inside of the wrench is the “size” of the wrench.

What is a size 10 wrench?

The metric wrench size 10 is the same as a US size 3/8 wrench. This size wrench is meant for a bolt with a diameter of “3/16” inches or 5mm.

What size is a 14-wrench?

A metric size 14 wrench does not have an equivalent US size. This size wrench is meant for a bolt with a diameter of 8mm.

Is 3/4 and 19mm the same?

If we are talking about the bolt size, yes they are the same. The bolt of size 3/4 is the bolt of size 19mm. However, if we are talking about the wrench size to work on the bolt, then they are not. The wrench marked 3/4 is the same as the wrench marked 21, and the wrench marked 19mm is the same as the wrench marked 5/8.


American wrench sizes are marked inches and the rest of the world are usually in millimeters. Several toolboxes or sets will usually include some sort of chart to help with the conversion and some even go as far as printing both the sizes on the wrenches. They print the imperial units on one side and the metric on the other side. The size of the average wrench is easy to eyeball once you use it for a while.

We wish you a tight hand on your next fitting project. It will be a great gift if you share this article after leaving a comment.

Picture in this post is by Matt Artz on Unsplash

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