How To

Tape Measure Markings – What Do They Mean?


23rd June 2015

Whilst many of you will think you know how to use a tape measure, do you actually know how to use all of it? Do you know what the odd selection of markings refer to that are usually found within the first 20cm of a tape’s length?

The UK Government’s Measuring Instruments (Material Measures of Length) Regulations implemented the European Measuring Instruments Directive (MID) in 2006. In order to comply with these regulations it became a legal requirement for manufacturers (with a few exceptions) to include a number of markings along the length of their blades. This article should help you understand what they are and how they should affect which tape measure you choose to buy.

If you want to learn more about tape measures and, in particular, how to read them properly, why not check out some of our other articles?

Other Articles

Metric and Imperial Markings

Whilst some countries such as the USA still focus primarily on Imperial or ‘English’ markings (feet, inches, yards etc.), most countries have moved onto the metric system. The UK, however, still uses a combination of the two – the mandatory metric system as enforced by the European Union and the more traditional Imperial system still in use by many trades.

Tape Measure Markings

Roman Numerals for Accuracy

Pull the blade out of the case and you may notice a Roman numeral within either a circle or a rectangle, generally printed in red or black. This refers to the accuracy of that particular tape.

There are four generally accepted levels of tape measure accuracy. Class 1 (denoted by the Roman numeral ‘I’) is the most accurate. Class 2 (denoted by ‘II’) the second most accurate with Class 3 (III) logically being the third. Unclassified tapes will not feature any marking on their blade. By ‘unclassified’ we mean that they have not been tested and guaranteed to conform to a particular level of accuracy.

Class 1 tapes are becoming more and more popular, especially amongst those who demand absolute precision in their work. That said, most everyday and professional tape measures on the market today (including everything from Stanley, Irwin, Draper, Bahco and more) are EC Class II accurate. When used properly Class II tapes are more than accurate enough for the vast majority of users.

You can learn more about the difference between Class 1 and Class 2 tape measures by reading our article – The Advantages of a Class 1 Tape Measure.

Tape Measure Accuracy


Whilst the length of most tapes is printed on the case, it is a legal obligation for manufacturers to print it on the blade as well. The length must be printed on each scale – one for metric and one for imperial.

Tape Measure Length

Black Diamonds

By far the most common question asked by our customers is “what do the little black diamonds mean?” Even though they’re not commonly used in the UK, these marks are still worth explaining.

The black diamonds, as they’re commonly called (sometimes shown as black circles instead), are actually stud or joist marks. Whilst not featuring on all tapes, stud marks frequently appear at 16” intervals and joist marks at 19.2” intervals.

The centre of one stud is generally positioned 16 inches from the centre of the stud before it – hence the 16” stud mark. Joists, on the other hand, are generally spaced 19.2” inches from the centre of the joist before it. Whilst this may seem to be a pretty odd measurement, many American building materials (such as boarding etc.) typically come in 8ft lengths. 19.2” divides perfectly (5 times) into 8ft.

Stud Marks

Year of Manufacture

On many tapes (but by no means all) you will find a small red rectangle with the letter M printed inside followed by a number. The number simply denotes the year that the blade was stamped as conforming to the Measuring Instruments Directive. On the whole this will also be the year in which that tape was manufactured. M09 generally signifies a tape measure that came off the production line in 2009 whilst M13 (as seen in the picture below) shows a tape most likely manufactured in 2013.

Year of Manufacture

CE Mark

The CE mark indicates that the tape measure conforms to all European Union regulations that apply to it. In the case of tape measures that means the European Measuring Instruments Directive (MID). This doesn’t mean that it was manufactured in the EU but is, to a certain extent, an indicator of quality.

Please note that the lack of a CE mark in no way indicates a tape measure of poor quality. It could simply mean, for example, that the blade is of a slightly older design which in no way affects its accuracy or quality.

CE Mark

Temperature & Tension

Many tape measures feature the marks ‘20°C’ and ‘50N’ near to the tip of the blade. This relates to the tape measure’s quoted level of accuracy. EC levels of accuracy (Class 1 or Class 2) state that a tape’s blade is accurate to that particular standard at a temperature of 20°C at a pulling force of 50N (Newtons). 20°C being the temperature of the laboratory where the accuracy of the blade is tested.

If the tape measure is being used in temperatures other than 20°C or at a pulling force of more/less than 50 Newtons then the accuracy of that tape cannot be guaranteed. Whilst that doesn’t necessarily mean that the tape’s accuracy has been affected, the user will have to satisfy themselves of this and may have to manually compensate for that change in temperature and/or force. Information on how to do this can be found on Wikipedia by searching for ‘tape correction’.

Testing Body

The four digit number (generally 0126 for tape measures) relates to the agency responsible for issuing the certification. 0126 is the designation for the National Weights & Measures Laboratory in Middlesex.

Testing Body

Other Markings

A number of other symbols can be printed in the first 20cm of the blade depending upon the individual manufacturer. Some tape measures will include the calibration number provided by UK Weights and Measures and some will feature a batch number to further help the manufacturer identify a product’s build date.

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