How many tubes?
Measure the joint, pick the bead size, and we'll do the geometry. Nobody wants to run out halfway down a tub, and nobody needs eleven tubes for a window.
How the math works
A bead is a long, thin solid, so its volume is its cross-section times its length. The profile decides the cross-section:
- Corner fillet: the triangular bead you run where a tub meets tile or a baseboard meets a wall. Area is half the bead size squared.
- Square gap, full depth: a slot filled all the way down, as deep as it is wide. It uses more caulk than you'd think, and deep joints like this are exactly where backer rod saves you tubes.
- Over backer rod: the pro method for wide joints. Sealant depth equals the width up to 1/2 inch, then half the width, and never less than 1/4 inch. Check the tube; some sealants specify their own depth rules.
A standard 10.1 fl oz cartridge holds about 18 cubic inches of sealant. You won't get every drop out, and some goes on your fingers, which is what the waste allowance covers.
Not sure what to buy? The Caulk Finder will name the formulation and a tube.