Caulk Calculator

Caulk quantity is determined by the joint dimensions (width and depth) and the total linear feet to be sealed. A simple formula tells you how many tubes to buy.

Volume per Linear Foot Formula:

Volume (cu in/ft) = Width (in) × Depth (in) × 12

Tubes Required:

Tubes = Total Volume (cu in) / 18.6

The standard North American cartridge is 10.3 fluid ounces, which is 18.6 cubic inches. That is the figure this page uses everywhere. You will still see “10 oz tube” written all over the internet, but a genuine 10.0 fl oz cartridge holds 18.05 cu in, about 3% less, and mixing the two numbers is where most caulk estimates start drifting. European cartridges are usually quoted as 300 ml, which is 18.3 cu in, close enough that the answer here works for both.

Worked example, a bathtub surround:

Perimeter of tub: 12 linear feet of joints
Joint width: 0.25 inch
Joint depth: 0.25 inch
Volume/ft = 0.25 × 0.25 × 12 = 0.75 cu in/ft
Total volume = 0.75 × 12 = 9 cu in
Tubes = 9 / 18.6 = 0.48, and with the 10% the calculator adds for waste, 0.53, so buy 1 tube

The 10% is not fussiness. You lose a surprising amount to the nozzle, to the first inch of every new bead while you find the pace, and to the section you tool badly and scrape out.

The 2 to 1 rule, and why joints fail

For a joint that moves, sealant makers ask for a depth of about half the width, kept between about 1/4 and 1/2 inch (6 to 12 mm), and never more than the width. On a narrow joint the 1/4 inch floor wins, which is why the tub joint above can sit 1/4 inch deep without trouble. A caulk bead has to stretch as the joint moves, and a bead that is deeper than it is wide cannot stretch, so it tears away from one face instead. This catches people out on deep gaps: the instinct is to fill the void, and filling the void is exactly what makes it fail.

For anything deeper than about half an inch, push closed-cell backer rod in first until the remaining depth is right, then caulk over it. Backer rod costs almost nothing, stops caulk bonding to the back of the joint (which is what lets it stretch properly), and saves you tubes.

Coverage by joint size (per 10.3 oz tube, before waste):

Every row in that table is a square joint, width equal to depth, because that is how the coverage figure is normally published. Read the 2 to 1 rule above and you will notice the rows from 3/8 inch up are deeper than they should be. A 1/2" gap tooled to 1/4" deep over backer rod covers 12.4 ft per tube, double the table, and it outlasts the square bead by years.

If your joint is one of the standard widths and you would rather not work the depth out, the Caulk Tube Coverage Calculator linked below applies the rule for you and compares the widths side by side.

Caulk types by application:

Application tips: Never caulk a dirty or damp surface. Adhesion fails within weeks, and it fails invisibly, so the first sign is usually water damage behind a bead that still looks fine. Clean with rubbing alcohol, let it dry completely, then apply. A smooth pass with a wet finger produces the slightly concave bead that sheds water properly.

Cut the nozzle small. You can always cut more off, and a nozzle opened to the full width of the joint gives you a bead you cannot tool without smearing it across the tile.