Things You'll Need
Instructions
Measure the steel shell. Flip the helmet upside down and use a tape measure to measure the circumference of the inside of the steel shell, below the lining, along the three rivet holes. If you only have a ruler you can use string to measure the length of the circumference, then use the ruler to measure the string. German helmets were made in even sizes, 60, 62, 64, 66, 68, 70 and 72 centimeters. Sizes 62 through 68 are the most common to find as collectibles today.
Check the rim of the helmet. Original German helmets will have the size of the steel shell printed inside the rim. You will see two letters followed by the size of the helmet. Even if you are able to read the stamp, it is smart to measure the helmet yourself to ensure that you are reading the size correctly. The stamping is usually not crisp and often will have worn in the years since printed.
Measure the inner lining band. Use your tape measure to measure the circumference of the inside of the lining of the helmet. The sizes of linings produced were 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, and 63 centimeters.
Measure your head. If you bought a helmet that no longer has a lining, you can order a replacement for it. There are many sites online that sell them new, or you may be lucky enough to find one at an antique store or an auction. To order, you will need the shell size and your head size. Simply use your tape measure to measure the circumference of you head, above your ears, in centimeters. This number will directly correspond to the sizes of linings that were produced.