How to use this calculator
- 1Add up the total length of all the joints you want to seal.
- 2Choose the joint shape: a gap between two surfaces, or a triangular bead in a corner.
- 3Enter the width and depth of the sealant. For gaps, the depth is usually about half the width.
- 4Pick your cartridge size, or type the volume printed on the tube.
The formula
- 01Cross-section = width × depth (× ½ for a corner bead)
- 02Sealant = total length × cross-section × (1 + extra %)
- 03Cartridges = sealant ÷ cartridge volume, rounded up
- 04Length per cartridge = cartridge volume ÷ cross-section
A joint of sealant is a long, thin strip, so its volume is its length times its cross-section. A 6 × 6 mm joint has a cross-section of 36 mm², so one 310 ml cartridge fills about 8.6 m. In US units, a 1/4 × 1/4 in joint takes 1/16 in², and a 10.1 fl oz cartridge (about 18.2 in³) fills about 24 ft — the same figure sealant makers print in their coverage tables.
A bead run into an internal corner, such as along a bath or a kitchen worktop, is roughly a triangle, so it uses half as much. The extra allowance covers the nozzle, sealant wiped off when smoothing, and what stays in the cartridge.
Worked example
Sealing 10 m of joints 6 mm wide and 6 mm deep takes 0.36 L of sealant.
A cartridge of 310 ml fills about 8.61 m of this joint, so with 10% extra you need 2 cartridges.
Tips before you buy
- Cut the nozzle at 45° to a slightly smaller opening than the joint width — you can always cut more off.
- Clean and dry the joint first and remove old sealant completely; new sealant does not stick well to old silicone.
- Mask both sides with tape for a neat line, smooth the bead, and pull the tape off before the sealant skins.
- Fill a bath with water before sealing it so the joint is sealed at its widest when the bath is in use.
- Choose the right sealant for the job: sanitary silicone for wet areas, paintable acrylic caulk for trim and cracks, polyurethane or hybrid sealants for outdoor and moving joints.
Frequently asked questions
How far does a tube of caulk go?
A standard 10.1 fl oz tube fills about 24 ft of a 1/4 × 1/4 in joint, and a 310 ml cartridge about 8.6 m of a 6 × 6 mm joint. A thinner bead goes much further: halving the width and depth quarters the sealant used.
How much caulk do I need for a bathtub?
A 1700 × 700 mm bath in an alcove has about 3.1 m (10 ft) of joint along the walls. A 6 mm triangular corner bead uses about 18 ml per metre, so one 310 ml or 10.1 fl oz cartridge is usually plenty — buy a second if the gap is wide or uneven.
What size should a sealant joint be?
For joints that move, sealant makers recommend a width about twice the depth, with the sealant at least 6 mm (1/4 in) and at most 12 mm (1/2 in) deep. Very narrow joints cannot stretch much, so they are more likely to tear.
What is backer rod and when do I need it?
Backer rod is a round foam cord pushed into deep gaps before sealing. It sets the sealant depth, saves sealant, and stops the sealant sticking to the back of the joint, which lets it stretch properly. Use it when a gap is deeper than about 12 mm (1/2 in).
How many ml is a standard caulk tube?
In the UK and Europe most cartridges hold about 300–310 ml; professional foil packs (sausages) hold 400 or 600 ml. In the US the standard tube is 10.1 fl oz (about 300 ml), with larger 20 fl oz sausages and 28 fl oz cartridges.
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Sources
- Sikaflex-1A product data sheet: yield per 10.1 oz cartridge, 2:1 width to depth, 1/4–1/2 in depth
- Tower Sealants caulk calculator: 10 % waste allowance
- Sikaflex-11 FC+: 300 ml cartridge and 600 ml foil pack
Formulas last reviewed: September 30, 2026 ·How we check our formulas