About this calculator
This calculator estimates how many cans of PU expanding foam you need to fill the installation joint around a batch of windows and/or doors, plus optional expansion tape and vapour(-open) tape for sealing the joint on the outside and inside faces.
Formula
joint length = sum over openings of 2 x (width + height) x count
joint volume = joint length x joint width x joint depth
joint volume (with waste) = joint volume x (1 + waste%)
cans required = ceil(joint volume (with waste) / can cured yield)
tape length = joint length
tape rolls = ceil(tape length / tape roll length)
Worked example
Three 1200 x 1400 mm windows and two 600 x 600 mm windows, a 15 mm wide x 50 mm deep joint, 30 L cured yield per can, 15% waste, 6 m tape rolls.
joint length = 3 x 2x(1.2+1.4) + 2 x 2x(0.6+0.6) = 15.6 + 4.8 = 20.4 m
joint volume = 20.4 x 0.015 x 0.05 = 0.0153 m³; +15% waste = 0.017595 m³
cans = ceil(0.017595 / 0.030) = 1
tape rolls = ceil(20.4 / 6) = 4
FAQ
Why is the can yield an estimate rather than a fixed number? Cured yield depends on the can's rated output, ambient temperature and humidity (foam cures by reacting with moisture in the air), and how deep and wide the joint really is compared with the manufacturer's test conditions. Enter the cured-yield figure from your specific product's data sheet if you have it; the default is only a common, rounded example.
Why does this calculator ask for expansion tape and vapour tape separately? They do different jobs and are not interchangeable: expansion (compression) tape on the outer face keeps the joint weathertight while allowing movement, and vapour(-open) tape on the inner face controls air and moisture flow so the wall build-up doesn't trap moisture in the foam. A job may use one, both, or neither, so each has its own on/off switch.
Which standard does this follow? None is cited. Foam cured yield and tape roll sizes are manufacturer data, not defined in a single technical standard; the volume calculation itself is plain geometry.
Assumptions and limits
Can cured yield, and both tapes' roll lengths, are user inputs with example defaults, not measurements of a specific product. The joint width and depth apply uniformly to every opening entered — a job with a genuinely different joint size per opening needs a separate calculation for that opening. No drawing is produced — the result is a materials list only.