Sealant Calculator
Enter the joint length, width, and depth to find out how many tubes or cartridges of sealant you need. Switch between metric and imperial units, add a waste percentage to avoid running short, choose your package size, and add a price to get a total cost estimate - all in one tool.
How to calculate how much sealant you need
The core formula is straightforward: multiply the joint length by its width and depth to get the volume of sealant required. For a rectangular gap this is V = L x W x D. For a triangular corner fillet the cross-section is a right-angle triangle, so the area is half of width times width: V = 0.5 x L x W x W. Once you have the net volume, divide by the package size (in the same units) and round up to the next whole number to get the tube count. Because sealant is wasted at start/stop points, uneven beads, and practice runs, always add a waste factor before dividing - 10% is a reasonable minimum, and 20% is safer on rough or irregular surfaces.
Choosing the right joint depth
Joint depth is as important as volume. Applying sealant too deep wastes product and can cause cracking as the sealant cures under tension. The industry rule of thumb is 1:1 depth-to-width ratio for joints up to 12 mm wide: a 10 mm wide joint should be 10 mm deep. For wider joints (over 12 mm) switch to a 1:2 ratio - a 20 mm wide joint needs only about 10 mm of sealant depth. Achieve the correct depth by first pressing a foam backer rod into the joint; the rod also prevents three-sided adhesion (bond-breaking), which is the main cause of sealant failure in movement joints. Using a backer rod on a 20 mm wide joint can cut sealant consumption by 40 to 50% compared with filling the joint solid.
Package types and how to compare them
Sealant is sold in several container formats. Standard cartridges (290-310 mL) fit a basic caulk gun and suit most domestic jobs. Larger foil sausages (600 mL) require a compatible extrusion gun but are more economical per millilitre on bigger projects and produce less solid waste. Quart jars and gallon pails are used for brush-applied or specialty sealants. When comparing products, always calculate cost per millilitre rather than cost per tube, since package volumes vary. This calculator shows the number of packages in your chosen format so you can compare options directly.
Waste, over-ordering, and common mistakes
Every caulking job involves some unavoidable waste. The nozzle tip must be cut to size and primed before the first bead, joints often need two passes, and misapplied sealant must be wiped off immediately (uncured) or cut out (cured). A 10% waste factor is the bare minimum for experienced applicators on clean, straight joints; use 15-20% for DIY work on irregular surfaces or when working in awkward positions. Over-ordering slightly is almost always the right choice - unused cartridges can often be returned or stored for touch-ups, but running out mid-joint means the seam must be cut back and redone.
Recommended joint dimensions and sealant yield
| Joint width (mm) | Recommended depth (mm) | Depth rule | Typical use |
|---|---|---|---|
| 4 | 4 | 1:1 | Glazing, small cracks |
| 6 | 6 | 1:1 | Window frames, door frames |
| 8 | 8 | 1:1 | Interior expansion joints |
| 10 | 10 | 1:1 | Flooring perimeter joints |
| 12 | 12 | 1:1 | Exterior cladding joints |
| 15 | 8 | 0.5:1 (backer rod) | Wide exterior joints |
| 20 | 10 | 0.5:1 (backer rod) | Facade expansion joints |
| 25 | 12 | 0.5:1 (backer rod) | Heavy structural joints |
Industry guidelines for rectangular gap-fill joints. Use these as starting dimensions; adjust for your actual gap.
Frequently asked questions
How do I calculate how much caulk I need?
Measure the total length of the joint in metres (or feet), then measure the width and depth of the gap in millimetres (or inches). Multiply all three together to get the volume. Divide by 1000 if you measured in millimetres to get millilitres. Add 10-20% for waste, then divide by the package volume (typically 310 mL for a standard cartridge) and round up to find the number of tubes to buy.
How many linear metres does one cartridge of sealant cover?
It depends entirely on the joint size. A standard 310 mL cartridge fills about 31 metres of a 5 mm wide by 2 mm deep joint, but only about 3.4 metres of a 10 mm x 9 mm joint. Use this calculator to find the exact coverage for your joint dimensions.
What is the difference between a rectangular joint and a triangular fillet?
A rectangular joint is a gap filled with sealant to a set width and depth - used for window frames, expansion joints, and cracks. A triangular fillet is a bead of sealant applied in an internal corner (where two surfaces meet at roughly 90 degrees), forming a triangular cross-section. Because only half the rectangular area is filled, a triangular fillet uses about half as much sealant as a rectangular bead of the same width.
Should joint depth equal joint width?
For joints up to 12 mm wide, yes - use a 1:1 depth-to-width ratio. For wider joints, use about half the width as the depth (a 1:2 ratio) and install a foam backer rod first to control depth and prevent the sealant bonding to the back of the joint. Excess depth wastes product and makes the sealant more likely to crack when the joint moves.
What waste factor should I use?
Use at least 10% for professional applicators on clean, regular joints. Add 15% for rough or irregular surfaces. Use 20-25% for DIY projects, tight angles, or whenever you are working above head height. It is cheaper to buy one extra tube and not need it than to run out halfway through a joint and have to restart.
Can I store unused sealant cartridges?
Yes. Seal the nozzle tip immediately after use by covering it with tape or a plug. Most silicone and polyurethane sealants remain usable for 6-12 months in a cool, dry location as long as the cartridge has not been punctured at the foil end. Check the manufacturer expiry date before reusing stored product.