How many metres does a cartridge of sealant or adhesive actually do?
Coverage is decided by the cross-section of the bead, which changes with the square of the nozzle size — which is why a slightly bigger nozzle halves the length you get.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 3 min
Short answer
A cartridge holds a stated volume, and the length of bead you get is that volume divided by the cross-sectional area of the bead. Doubling the bead width roughly quarters the run. As a rule of thumb, a standard cartridge does a long run at a fine bead and only a few metres at a fat one, so measure the joint and cut the nozzle to the width you actually need.
This is one of the few genuinely arithmetic questions in the whole subject, and it explains a lot of frustration on site. People buy one cartridge for a bathroom, cut the nozzle generously, and run out halfway down the second wall. The nozzle cut, not the brand or the length of the run, is what decides it.
Step by step
- Find the volume on the cartridge.It is stated in millilitres, and the common household sizes cluster around a few standard volumes. Foil sausage packs hold considerably more than a rigid cartridge and need a cradle gun.
- Work out the bead cross-section you actually need.Measure the joint width. The bead should fill the joint, so its cross-section is roughly the joint width multiplied by the depth you intend, which for a properly proportioned joint is about half the width.
- Divide the volume by the cross-section.Volume divided by cross-sectional area gives length. Keep the units consistent — millilitres are cubic centimetres, so working in centimetres throughout gives an answer in centimetres of bead.
- Understand why the nozzle matters so much.Bead area goes up roughly with the square of the bead width. A bead half again as wide has more than double the cross-section, so you get less than half the run out of the cartridge. This is why cutting the nozzle small is both a quality decision and an economic one.
- Add a real allowance for waste.The first squeeze, the last of the cartridge that will not extrude, the run you had to cut out and redo, and the material lost to tooling. Twenty per cent on top of the calculated figure is not generous.
- Buy one more cartridge than the calculation says.Running out halfway along a run means a visible join, because a bead restarted after the cartridge has been swapped almost never matches. The spare cartridge is cheaper than the join.
- Apply the same logic to grab and construction adhesive.The same volume divided by the same geometry, except that the beads are usually applied as vertical zigzags or spots rather than a continuous line, so estimate the total length of bead you will lay rather than the length of the item.
- Check the manufacturer's own coverage figure if there is one.Many cartridges print a table of bead diameter against length. It is calculated the same way and it saves the arithmetic.
Tips
- Cut the nozzle smaller than you think and enlarge it if you must. You cannot uncut it, and every millimetre costs you run length.
- Foil sausage packs are much cheaper per unit volume and produce far less waste plastic, and they need a cradle gun. On any large job they are worth the gun.
- Buy all the cartridges you need from the same batch where colour matters. Whites and greys do vary slightly between production runs, and a joined run shows it.
- For a bathroom, measuring the total length of joint first takes two minutes and prevents both the second trip to the shop and the visible join.
- Part-used cartridges have a short life. Buying two large ones when three small ones would fit the job is usually false economy.
Questions people ask
How much silicone do I need for a bathroom?
Measure the total length of every joint — bath, tray, basin, worktop, screen — and work out the bead width each needs. A typical bathroom is a surprisingly long total run, and it is worth doing the sum rather than guessing.
Why did my cartridge run out so quickly?
Almost always the nozzle was cut too large. Bead volume rises with the square of the width, so a modest over-cut can halve the run you get.
Is a foil sausage pack better value?
Per unit volume, considerably, and it produces much less waste. It needs a cradle or sausage gun, so it makes sense once you are doing more than the occasional joint.
How much grab adhesive does a cartridge cover?
It depends entirely on bead size and spacing. Estimate the total length of bead you will actually lay — the zigzags and spots, not the length of the board — and apply the same volume calculation.