How we calculate sizes

Method version 0.3 · Last reviewed: 2026-10-05

This page is the entire method. Take any number we publish, read the rules below, and you should be able to arrive at it yourself.

Step 2 — Functional Allowances

Product	Measurement	Formula & Reason
Harness	girth_cm	girth_expected + 5cm. Explains why harness sizing cannot be guessed from weight and details common chafing issues in deep-chested breeds.
Collar	neck_cm	neck_expected + 4cm. Reminds owners of short-necked breeds to choose wider bands to prevent slippage.
Crate	length_cm, height_cm	length >= length_expected + 8cm; height >= height_expected + 8cm. Greatest divergence category: long-backed short-legged breeds receive significantly longer crates than weight would indicate.
Bed	length_cm	*diameter >= length_expected 1.25**. Distinguishes curled and stretched sleeping styles with tailored dimensions.
Travel Carrier	length_cm, height_cm	Dual-verified against airline cabin limits and body length. Strongest differentiator: the same dog may fit airline A cabin regulations but exceed airline B.
Coat & Apparel	length_cm, girth_cm	Back length sets base size; chest girth determines relaxed fit. Thermal insulation varies drastically between single and double coats; the decision to clothe differs even at identical body sizes.

Step 3 — Standard Size Bands

The measured requirement is mapped onto standard size bands for that product category. Our bands, including exact centimeter ranges behind each size, are published on our category guides, such as our harness sizing guide.

Step 4 — Category-Specific Boundary Rules

Snug-fit products (Harness / Collar): Your measurement sits within 2 cm of a boundary. If it falls inside a size, that is your size — but prefer an item with adjustable straps so you can fine-tune the fit.
Clearance products (Crate / Bed): Take the larger size to guarantee adequate interior room.