Caulk Calculator
Estimate how many tubes of caulk or sealant you need from the joint length, width and depth — 300 mL cartridges, 10.1 oz tubes or sausages — with the right depth ratio, bead length per tube and backer rod size.
How it works
sealant (mL) = width (mm) × depth (mm) × length (m) × (1 + waste) · cartridges = sealant ÷ cartridge volume (rounded up) · bead length per cartridge = cartridge mL ÷ (width × depth) metres
A sealant joint is a rectangle in section, so the volume is width × depth × length; with millimetres and metres the result comes out directly in millilitres. ASTM C1193 guidance is a depth equal to the width for joints up to about 12 mm (½ in) and half the width for wider joints, never less than 6 mm, controlled with a closed-cell backer rod about 25% wider than the joint so it stays compressed. A 300 mL cartridge runs about 8 m of a 6 × 6 mm bead or 3 m of a 10 × 10 mm bead. Add waste for tooling, nozzle cut-off and the last bit left in the tube.
Worked example
Sealing 20 m of 6 mm joints, 6 mm deep, with 10% waste: 6 × 6 × 20 × 1.1 = 792 mL, so 792 ÷ 300 = 2.6 → 3 cartridges of 300 mL. Each cartridge runs 300 ÷ 36 = 8.3 m of bead; use 8 mm backer rod in deeper gaps.
Sources: ASTM C1193 Standard Guide for Use of Joint Sealants · Sealant, Waterproofing & Restoration Institute — Sealants: The Professionals’ Guide
Frequently asked questions
How many feet does a tube of caulk cover?
For square joints (depth = width), a 10.1 oz (299 mL) tube runs about 97 ft of a ⅛″ bead, 43 ft of ³⁄₁₆″, 24 ft of ¼″ and 11 ft of ⅜″. Half-depth joints go twice as far.
How deep should a caulk joint be?
About as deep as it is wide up to ½″ (12 mm), and half as deep as it is wide for wider joints, but at least ¼″ (6 mm). Too deep wastes sealant and makes the joint stiff.
What size backer rod do I need?
About 25% bigger than the joint width so it stays wedged in: 8 mm rod for a 6 mm joint, 13 mm for 10 mm, 16 mm for 12 mm and 25 mm for 20 mm joints.
How many metres does a 300 mL cartridge of silicone cover?
About 33 m of a 3 × 3 mm bead, 8 m of 6 × 6 mm, 3 m of 10 × 10 mm and 1.2 m of a 20 × 12 mm expansion joint.
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This calculator is for educational purposes. Double-check important results before acting on them.