Find your helmet size

GDM Motorcycle Helmets Size Chart

Measure around your head, enter the number, and get the GDM size to order. Adult and youth sizes, in centimeters, inches, or hat size.

Measure your head

Who is the helmet for?

1Measure

Wrap a soft tape around the widest part of the head, about 1 in (2.5 cm) above the eyebrows and just over the ears. Keep it level and comfortably snug. Measure twice and use the larger number.

2Enter the measurement

Head circumference

Drag the tape or type a number. Hatched gaps fall between sizes, where GDM recommends the larger size.

MMedium See details ↓

Your GDM size

Example

Medium

Centimeters: 57–58
Inches: 22 1/4–22 7/8
Hat size: 7 1/8–7 1/4

Where you fall in Medium22 1/2 in

57 cm · roomiersnugger · 58 cm

See helmets in Medium

Adult size chart

GDM helmet sizes by head circumference
Size	Head (cm)	Head (in)	Hat size

Between sizes? Order the larger size. The chart is for reference only. Always try the helmet on and follow the fit check below.

How to measure

Wrap a soft cloth measuring tape around the head about 1 in (2.5 cm) above the eyebrows, just over the ears, and around the widest part of the back of the head.
Keep the tape level all the way around and pull it comfortably snug, not tight.
Read the number where the tape overlaps. Measure two or three times and use the largest measurement.
Match it to the chart. If you fall between two sizes, choose the larger one.

No soft tape? Wrap a piece of string or a charging cable the same way, mark where it meets, then lay it flat along a ruler or a hardware tape.

Check the fit when it arrives

It feels snug and even all the way around, with the cheek pads lightly pressing the cheeks.
There are no pressure points, especially across the forehead.
With the strap fastened, the helmet doesn't shift or rotate when the rider shakes their head.
Wear it indoors for 5 to 10 minutes before riding. If the rider wears glasses, try it with them on.
New pads feel tight at first and break in after a few rides.

Head shape: GDM helmets are built for a neutral to slightly oval head shape, which spreads pressure evenly and reduces hot spots.

Helmets in your size

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GDM Motorcycle Helmets Size Chart

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