If you'd like a collar that's simple and wears very well in the field, this is a good choice for you.
Brown Harness Leather Chain Martingale I (20")
Medium brown harness leather chain martingale collar; Large stainless steel 3 ring assembly chain; 1" width tapering; 20" inner circumference
Because the chain martingale collar needs to slip over your dog's head, you need to measure the largest point BEFORE it slips onto and over the ears. Using a flexible tape measure is helpful. The measurement around the head will be the inner circumference or inner measurement of the collar. Be careful to avoid fingers under the measuring tape. Remember that it is easier to slide a collar over the head and onto the neck than to pull it off.