Read the deflated measurements
Separate diameter, girth and length before comparing products.
Compare the same measurements
Diameter is the width across the relevant section. Girth measures around it. Ask where a manufacturer measures if the listing does not say.
Start with the deflated size
The deflated width matters even when the listing emphasizes expansion. Compare that figure first and ask for it if it’s missing. Published dimensions are descriptions, not recommended amounts of expansion.
Keep length and width separate
A change in length and a change in diameter are different. For the same distinction in noninflatable designs, see the bead measurement guide.