For your pet's safety & comfort, please measure for a collar by measuring your pet's neck. As a general guide, you should be able to fit two fingers (flat) easily between the tape & your pet's neck.Remember , a collar shouldn't be tight around your pet's neck & it wouldn't be the exact measurement of your pet's neck. But for safety reasons.....So it doesn't snag on something, it shouldn't be too loose either. A snug fit is what your are aiming for, not a tight one or one that chokes.