Ombraz have no arms — an adjustable cord runs around the back of your head instead, and Ombraz state the cords fit all head sizes. What you're choosing when you pick a size is the width of the frame across your face. Regular fits about 80% of customers.

Ombraz's own check is the credit card test: hold a card on its edge against the centre of your nose, pointing out toward your eye. If it roughly touches the corner of your eye you're a Regular; past the corner, look at Narrow; short of it, look at XL.

• Regular fits most people — Ombraz say 80% of their customers wear Regular.
• Credit card test: touches the corner of your eye = Regular; extends past it = Narrow; doesn't reach = XL.
• Start with the cord loose, place the frames on your nose, guide the cord above your ears, then pull the adjusters gently apart.
• You should be able to pull the frames 2–3cm from your face before the cord goes taut — you shouldn't feel pressure from the frames or cord.
• Wearing a hat or helmet? Run the cord over the top of it.