Building & renovation
How many cans of spray foam do you need?
Number of 750 ml polyurethane foam cans from joint length, width and depth.
Quick answer
Expanding polyurethane foam is sold in 750 ml cans but priced by expanded volume — a typical can yields ~40–50 liters of cured foam, not the liquid you see in the nozzle. The gap geometry drives everything: a 2 cm × 5 cm slot along 12 m is far more liters than a shallow crack looks.
Advanced settings
Cans (750 ml) needed
1
- Foam volume needed
- 12 L
Figures are for polyurethane expansion foam in standard 750 ml cans. Deep gaps may need two passes; follow the manufacturer cure time before trimming.
How it works
Deep gaps may need two passes once the first expansion cures — the calculator gives cans for one fill at your stated depth. Default yield 45 L expanded per can is editable in advanced. Pair with polyurethane expanding foam and a foam gun if you are doing more than two cans — guns waste less than straw applicators.
Polyurethane foam does not cure by drying — it cures by reacting with moisture, so foam sprayed into a dry gap in a dry room sets hard on the outside and stays soft and crumbly in the core, which is why a joint that looked perfect can be dug out with a finger a month later. Mist both surfaces with water before you fill, and mist the surface of the bead afterwards. Second rule: fill about a third to a half of the gap depth, never the whole thing. It roughly triples, and a slot filled to the brim will bow a door frame or a window jamb hard enough that the door stops closing.
Frequently asked questions
How many cans for window installation gaps?+
Measure the perimeter gap: e.g. 12 m length × 2 cm width × 5 cm depth ≈ 12 L expanded foam before waste — often one can at 45 L yield. Uneven gaps or overfilling for trimming can need two.
Can I use foam to insulate a whole wall cavity?+
Handheld cans are for small gaps and sealing — not for full cavity fill (that needs professional PU kits and fire-rated assemblies). This tool sizes DIY gap volumes only.
Why did I need more cans than calculated?+
Common reasons: overstated yield on the tin, foam escaped before curing, or depth was deeper than measured. Cold cans expand less — store at room temperature before use.
Is foam waterproof?+
PU foam is water-resistant when cured but UV-degrades if left exposed — paint or seal per manufacturer. It is not a structural filler; deep loads need backer rod plus sealant, not foam alone.
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