How the caulk calculator works
A tube of sealant is a fixed volume, and a joint is a long, thin prism. Multiply the cross-section of the joint by its length and you have the volume to fill. A useful shortcut in metric: metres × millimetres × millimetres gives millilitres directly, so a 1 m joint of 6 × 6 mm holds 36 ml.
Cartridges = length × width × depth × shape factor × 1.10 ÷ cartridge volumeThe shape factor is 1 for a gap between two parallel surfaces (a movement joint, a gap round a window frame) and 0.5 for a triangular fillet run into an internal corner, such as along a bath or a worktop upstand. The extra 10% is what stays in the nozzle, the plunger dead space and the excess wiped off when you tool the bead. Imperial sizes are converted to millimetres (1 in = 25.4 mm) and the result shown in US fluid ounces.
Worked example
Resealing a kitchen and bathroom adds up to 20 m of joints, each 6 mm wide and 6 mm deep. The section is 36 mm², so the volume is 20 × 36 = 720 ml, or 792 ml with the allowance. A 300 ml cartridge runs 300 ÷ 36 = 8.3 m, so you need 2.64 cartridges – buy three. Had those same joints been triangular corner beads, the volume would halve and two cartridges would do. In inches: a 1/4 × 1/4 in bead from a 10.1 oz tube runs about 24 ft, so 65 ft of it takes three tubes.
How far one cartridge goes
| Bead (width × depth) | 300 ml cartridge | 10.1 oz cartridge |
|---|---|---|
| 3 × 3 mm (1/8 × 1/8 in) | 33 m | about 96 ft |
| 6 × 6 mm (1/4 × 1/4 in) | 8.3 m | about 24 ft |
| 10 × 6 mm (3/8 × 1/4 in) | 5 m | about 16 ft |
| 12 × 6 mm (1/2 × 1/4 in) | 4.2 m | about 12 ft |
| 20 × 10 mm (3/4 × 3/8 in) | 1.5 m | about 5 ft |
Figures are for a full rectangular joint; double them for a triangular corner fillet.
Getting the joint geometry right
- Width-to-depth ratio. A sealant stretches best when it is about twice as wide as it is deep. A 20 mm gap should be filled only 10 mm deep, not 20.
- Backer rod for deep gaps. Push closed-cell foam rod into anything deeper than about 12 mm (1/2 in). It sets the depth, saves sealant and stops the bead bonding to the back of the joint, which would tear it.
- Pick the right product. Silicone for wet areas around baths, showers and sinks; paintable acrylic caulk for skirting, architraves and cracks you will paint over; hybrid polymer where you need both adhesion and flexibility outdoors.
- Cut the nozzle to the bead. Cut at 45° slightly narrower than the gap; an oversized hole wastes material and leaves a messy line.
- Clean and dry first. Old silicone must be removed completely; new sealant does not bond to it. Fill a bath with water before sealing so the joint cures at its widest.
Frequently asked questions
How many feet does a tube of caulk cover?
A 10.1 oz cartridge runs about 24 ft at a 1/4 in × 1/4 in bead, about 48 ft at 1/4 × 1/8 in and only about 12 ft at 1/2 × 1/4 in.
How many metres of silicone in a 300 ml tube?
About 8 m at 6 × 6 mm, 16 m for a 6 mm triangular bead in a corner, and roughly 33 m at 3 × 3 mm.
How many tubes of caulk do I need for a bathroom?
A bath, a basin and a shower tray usually total 8 to 12 m (25 to 40 ft) of triangular bead, which is one or two 300 ml or 10.1 oz cartridges of sanitary silicone.
How many tubes of caulk to do baseboards?
Along the top of baseboards the bead is thin, about 3 × 3 mm, so a 10.1 oz tube covers roughly 90 ft; a typical 12 × 12 ft room with 48 ft of baseboard needs one tube.
How deep should a caulk joint be?
About half the joint width for gaps over 12 mm (1/2 in), with a minimum of about 6 mm (1/4 in); use backer rod to set the depth in deeper gaps.
Last reviewed: 2026-09-27 · How we calculate