Spray foam set & kit calculator
DIY foam ships in kits with a labeled board-foot yield. Enter the board-feet you need and the yield printed on the kit and this rounds up to whole kits — because you cannot buy 1.7 of them.
Calculator
1,000 board-feet ÷ 600 bd-ft = 2 kit(s). Kit/set yields are labeled — confirm on the kit; nominal yield assumes ideal temperature and minimal waste.
Formula
kits = ceil(board_feet ÷ yield_per_set)
Always round up: a partial kit still means buying a whole one, and the last kit rarely stretches to its nominal yield once cans cool down.
Worked example
1,000 board-feet with a 600 bd-ft large kit is 1,000 ÷ 600 = 1.67, rounded up to 2 kits. The same 1,000 board-feet in 200 bd-ft small kits is 1,000 ÷ 200 = 5 kits. Small kits cost more per board-foot, so on anything but a spot job the large kits usually win — but count the whole kits, not the raw ratio.
Why the real yield is lower than the label
Labeled yields are best-case. In the field, plan for less:
- Temperature. Cold tanks and a cold substrate cut yield hard. Kits want the cans and the surface warm; below spec, both output and cure suffer.
- Overspray and trigger waste. Purging, test sprays and the foam you shave flush all come off the total. A single kit rarely delivers its full number.
- You cannot pause a kit forever. Once opened, the chemistry has a working window. Do not buy so many that one sits half-used past its life — but do keep a small margin so you are not one kit short mid-job.
- Match kit size to the job. A rim joist or a small crawl suits a 200 bd-ft kit; a garage wall or a van build suits 600. Big jobs belong with a contractor rig, not a wall of kits.
Rule of thumb: size to your board-feet, round up, then add one small kit if the job is at all fussy. Running out at 90% done is the expensive mistake.
Reference table
| Kit / set | Labeled yield | Rough scope |
|---|---|---|
| DIY small kit | 200 bd-ft | A rim joist, a small crawl or spot-sealing |
| DIY large kit | 600 bd-ft | A garage wall, a van build, a bigger patch |
| Pro rig / bulk set | much larger | A whole attic or house — priced by the contractor |
Labeled DIY-kit yields are nominal — real yield drops with cold substrate, cold cans and overspray. Read the kit.
Frequently asked questions
How many spray foam kits do I need?
Divide your board-feet by the kit yield and round up. 1,000 board-feet with a 600 bd-ft kit is 2 kits; with a 200 bd-ft kit it is 5. Always round up to whole kits.
How many board-feet does a DIY kit cover?
Common labeled DIY yields are about 200 bd-ft (small) and 600 bd-ft (large), but the number is printed on the box and is nominal — use the kit's own figure and expect less in cold conditions.
Should I buy an extra kit?
Usually yes, a small one. Overspray, purging and cold cans eat into the labeled yield, and stopping the job to reorder is worse than a spare. Just do not overbuy past the kits' working life.
Is a kit cheaper than hiring a contractor?
For small, accessible jobs a kit can win. For a whole attic or house the per-board-foot cost of kits climbs fast — price it against a contractor with the spray foam cost tool.