The British MkII helmet is one of the most iconic pieces of military equipment from the Second World War. Worn by British and Commonwealth forces across Europe, North Africa and the Far East, millions were manufactured between 1938 and the end of the war. It was also where I first started collecting and it remains a firm passion of mine.
One feature that often surprises new collectors is that the steel helmet shell was produced in just one standard size. Rather than manufacturing different shell sizes, the British Army used interchangeable liners in a range of sizes to fit the individual soldier.
Whether you're restoring a helmet, replacing a damaged liner or simply trying to understand the size stamped inside your helmet, this guide explains how British MkII and MkIII helmet liner sizing works.
One Shell — Multiple Liner Sizes
Unlike German helmets, where both the shell and liner were produced in different sizes, British MkII and MkIII helmets used a single shell size.
The fit was determined entirely by the liner.
This made wartime production faster and simpler. If a soldier required a larger or smaller fit, the existing liner could simply be removed and replaced without changing the steel helmet.
This interchangeable system remained in use throughout the Second World War and continued for many years afterwards.
Understanding British Helmet Liner Sizes
Original British helmet liners are marked using the traditional British hat sizing system. Common examples include:
- 6¼
- 6½
- 6¾
- 7
- 7¼
- 7½
These measurements refer to the head size the liner was designed to fit. Today, most people measure their head in centimetres, so the conversion table below makes choosing the correct size much easier.
British MkII & MkIII Helmet Liner Size Conversion Guide
| British Liner Size | Head Size (cm) | Approximate Modern Size |
|---|---|---|
| 6¼ | 50 cm | XXS |
| 6⅛ | 51 cm | XXS |
| 6½ | 52 cm | XS |
| 6⅝ | 53 cm | XS |
| 6¾ | 54 cm | Small |
| 6⅞ | 55 cm | Small |
| 7 | 56 cm | Medium |
| 7⅛ | 57 cm | Medium |
| 7¼ | 58 cm | Large |
| 7⅝ | 59 cm | Large |
| 7½ | 60 cm | XL |
| 7⅝ | 61 cm | XL |
| 7¾ | 62 cm | XXL |
| 7⅞ | 63 cm | XXL |
| 8 | 64 cm | XXXL |
Please note: These are approximate modern equivalents. Original British Army helmet liners were manufactured using traditional British hat sizes, so we always recommend measuring your head and matching it to the liner size rather than relying solely on Small, Medium or Large.
How to Measure Your Head for a WW2 helmet
Measuring your head only takes a minute and will help you choose the correct liner size. Using a flexible tape measure:
- Measure around the widest part of your head.
- Position the tape approximately 1cm above your eyebrows.
- Pass the tape just above your ears and around the back of your head.
- Keep the tape snug but not tight.
Once you have your head circumference in centimetres, compare it to the conversion table above.
Where is the Size Marked?
The size is normally stamped directly into the liner itself. Depending on the manufacturer, this may be found:
- On the underside of the liner when out of a helmet
- Along the central cross-piece / bars
- Beside the manufacturer's details.
- Moulded into the fibre liner on later examples.
- On later Mk4 / Mk5 liners either on the red band or on a small cloth label.
If the stamp has worn away, measuring your head and comparing it to the liner and conversion table above is likely the easiest way to determine which liner you require. It is very fiddly to run a tape around the inside of a liner.
Which Sizes are Most Common?
The majority of original British and Commonwealth wartime helmets are found with liners in the following sizes: 6¾, 6⅞, 7, 7⅛ and 7¼. These sizes suited the majority of British servicemen.
Very small sizes below 6½ and large sizes above 7½ were produced in much smaller numbers and are considerably harder to find today.
Are MkII and MkIII Helmet Liners Interchangeable?
Yes. One of the advantages of the British helmet design was that liners could easily be exchanged between shells. This meant a damaged liner could be replaced without replacing the helmet itself, or a soldier could simply be issued with a different sized liner if required.
For collectors restoring original helmets, this makes finding the correct fit much easier. However, if originality is important, it is worth matching the date to the helmet shell whenever possible.
Original vs Reproduction Liners
Original wartime liners have now been around for over 80 years, so signs of age are perfectly normal. Collectors should expect to see:
- Wear to the leather sweatband.
- Ageing or cracking of the rubber cross or leatherette liner.
- Missing parts under the liner cross (No idea what their technical name is!)
Modern reproduction liners are widely available and are ideal for display or reenactment, but they are usually easy to distinguish from original wartime examples by their materials, stitching and markings.
We regularly stock original liners, parts and spares on our website. www.themilitariashop.com
Frequently Asked Questions
Were British Mk2 helmets made in different shell sizes?
No. Unlike German helmets, British MkII and MkIII helmets were produced with one standard steel shell size. Different fits were achieved by fitting liners in different sizes.
What does a WW2 size 7 helmet liner fit?
A size 7 liner is designed to fit a head measuring approximately 56cm in circumference, making it roughly equivalent to a modern Medium.
What is the most common British helmet liner size?
The sizes most commonly encountered today are 6¾, 6⅞, 7, 7⅛ and 7¼.
Can I swap the liner in my British helmet?
Yes. The liner was designed to be removable and interchangeable. This allowed soldiers to change sizes without replacing the steel shell.
Are MkII and MkIII helmet liners the same?
Yes they are interchangeable, although there are differences between manufacturers and production periods that collectors should be aware of when restoring an original helmet.
The only caveat here is a Mk3 helmet that has been converted to a Mk4 with the pull to dot fitting.
Why are British helmet liners marked in fractions?
British military helmet liners used the traditional British hat sizing system, which measured head diameter in inches rather than the circumference in centimetres.
How do I know what size liner I need?
Measure your head circumference using a flexible tape measure and compare the result with the conversion table above.
Are larger helmet liners rarer?
Yes. Sizes above 7½ are much less common than the standard wartime sizes and are generally harder to find. Anything over 8 is very rare indeed.
Do original helmet liners shrink?
Leather sweatbands can shrink slightly with age, particularly if they have been stored in very dry conditions. As a result, some original liners may feel tighter than their marked size.
Can I fit a reproduction liner into an original helmet?
Yes. Reproduction liners are widely available and will usually fit an original shell. They are an excellent option for display or reenactment, although collectors generally prefer original liners where possible.
Are Commonwealth helmet liners different?
British and Commonwealth manufacturers all worked to the same sizing system, so the liner sizes are interchangeable regardless of whether they were manufactured in Britain, Canada, Australia or elsewhere within the Commonwealth.
But, there are variations in the liners.
Does the helmet shell affect the size?
No. The shell is always the same size. It is the liner that determines the fit.
Final Thoughts
The British helmet was a simple yet highly effective design. By producing a single shell size and allowing the liner to be exchanged, the British Army simplified manufacturing, repairs and logistics while ensuring each soldier could be issued with a comfortable fitting helmet.
For today's collectors, understanding liner sizes makes it much easier to restore original helmets, identify replacement liners and choose the correct fit. We hope this guide has made the traditional British sizing system a little easier to understand.
If you're looking for an original British MkII or MkIII helmet, or a replacement wartime liner, be sure to browse our latest stock here at The Militaria Shop.
Further Reading
At The Militaria Shop, we’re collectors ourselves — and we know how much a good reference guide can help. We’ve been building out a library of guides covering everything from German helmet sizes and RZM codes to British uniform sizing and War Department stamps. We add new ones as we get the time, so there’s always something new in the works.
You can find all our guides on the Militaria Collectors Guides page, or browse a selection below.
