Cloth is sold by weight per metre. Light cloths travel well and feel cool; heavy cloths drape better and last longer.
A 260-gram worsted is the best all-year compromise for London. For the tropics, go lighter and choose an open weave like fresco or linen.
For a winter coat, nothing beats a heavy cloth of 500 grams or more. It will outlive you, and probably your son.
Twenty-six measurements, and the ones we don’t write down
Why it takes three fittings