What is the diamond on a tape measure? How to use this clever feature

Person measuring and marking wood with a pencil
(Image credit: Getty Images)

You might be wondering 'What is the diamond on a tape measure?' if you've ever noticed the tiny markings along the top edge of the tool.

The diamond has been part of the modern day tape measure for as long as we can remember and is one of the markings you will find alongside the measurements. That said, not every tape measure is the same. 

Here we reveal what the diamonds mean and what else you should look out for on a tape measure to make full use of your tool.

What is the diamond on a tape measure?

You will typically find a small black diamond on the top edge of your tape measure at regular intervals. On a UK tape measure the diamond is usually found every 19.2 inches along the tape. 

This diamond is essentially a joist mark, with joists generally spaced this far apart in UK structures. Joists are usually found in 19.2 inch intervals due to a lot of boards, such as plywood, commonly coming in eight feet (96 inch) lengths. 

When divided by five you get 19.2 inches, which works out as a good place for the centre of the joists to be positioned. This DeWalt tape measure is a good quality example if you want to use the diamond feature on your next project.

But to confuse the issue, some tape measures also include a diamond at 16 inch intervals, as seen in the below image. This measurement is typically used in the US. If you are learning how to build a partition wall in the UK the spacings are measured in millimetres.   

And to confuse matters further, the marking isn't always a diamond. Sometimes it is a circle instead.

Top down view of two Imperial/Metric tape measures side by side

Some Imperial/Metric tape measures have diamonds for common joist width and red markings for common US stud wall gaps. Some newer UK tape measures don't have the diamond. (Image credit: Steven Jenkins)

What are the red boxes at 16, 32 inches etc, used for? 

Some tape measures have a diamond every 16 inches, which is typically accompanied by a red box. In some cases there will only be a red box (with number) marking 16 inch gaps. This is the common measurement between studs in a stud wall in the US.

In the UK the standard measurement for a stud wall gap is 400mm. This is very close to 16 inches - 406mm - but obviously not the same. So if you are building a stud wall in the UK, these are best ignored.  

What does the metal end of a tape measure do?

The metal end on a tape measure – that is visible when the tape is fully retracted – is known as a hook. The obvious use is to hook it over the end of a surface and then pull out the tape measure to measure and mark.

Some tape measures have what is known as a nail grab as well, which is a little indent or hole to grab a nail or screw when needed. This is ideal when you need to measure from the centre of a joist or stud.

Some also have small teeth to scribe a mark if you don't have a pencil. If it doesn’t have teeth you can use the edge of the hook to make a mark. 

Close up of tape measure hook on wooden background

A tape measure hook often has a hole known as a nail grab where users can slot in the head of a nail or screw (Image credit: Steven Jenkins)

Why is the hook on the end of a tape measure loose? 

You have probably noticed that the hook on the end of your tape is a little loose. This is not a manufacturing error, it's meant to be like that. The tape measure is short by a sixteenth of an inch, which is the width of the hook. This means you get accurate readings when measuring the inside or outside of a surface.

If measuring the inside of a surface – maybe you have just finished painting windows and are measuring for blinds – the hook is pushed up against the tape to fill the sixteenth of an inch gap. If measuring the outside of a surface, the tape will pull out an extra sixteenth of an inch to give a precise measurement. 

What other tape measure marks should I look out for? 

One mark common to all tape measures is the length. This will be placed at the front end of the tape so you can see it immediately and it is typically in metres and feet. 

A few other marks you can find on a tape measure generally denote quality. A CE mark tells you that the tape conforms to EU regulations. Roman numerals indicate accuracy with level 1 being the best. 

If your tape measure doesn’t have one it means it hasn’t been tested to conform to a certain level of accuracy. But most brand names will have them, and even tapes without them are still good enough for general DIY jobs such as tiling a wall

Steve Jenkins

Steve is Homebuilding & Renovating's DIY content editor, and has been a writer and editor for two decades. He is an avid DIYer with over 20 years of experience in transforming and renovating homes. He specialises in painting and decorating, but has strong all-round building skills, having previously worked in the industry for 10 years.