Liquid waterproofing & air barrier calculator

1. Area to coat
   length × height
   40' 0" × 10' 0" = 400.00 SF
2. Coverage
   231 in³ ÷ (wet mils × 0.001 in) ÷ 144 = 1,604.17 ÷ wet mils
   1,604.17 ÷ 48 = 33.42
3. Gallons for the area
   SF ÷ coverage
   400 SF ÷ 33.42 = 11.97
4. Gallons in all
   field + detail
   (11.97 + 0) = 11.97
5. Containers
   gallons ÷ container size, rounded up
   11.97 ÷ 5 = 3

Where the numbers come from

• Coverage from mils: 1 US gal = 231 in³; at 1 mil (0.001") it covers 231 ÷ 0.001 ÷ 144 = 1,604.17 SF. Coverage = 1,604.17 ÷ wet mils; wet mils = dry mils ÷ volume solidsPure geometry from the exact US gallon (NIST). This is theoretical coverage on a smooth surface — the product data sheet and the project spec govern the thickness.Source
• Tremco ExoAir 230: Exterior sheathing / ICF: min 48 wet mils (25 dry), 33 ft²/gal · porous substrates: min 70 wet mils (35 dry), 23 ft²/gal · 5 gal pails, 52 gal drumsMath check: 1,604.17 ÷ 48 = 33.4 and ÷ 70 = 22.9 — both match the data sheet. The page uses the porous rate for concrete and CMU. Tremco says thicker application is acceptable.Source
• Henry Air-Bloc 33MR: 100 wet mils (55 dry), 55% solids by volumeMath check: 55 ÷ 100 = 55% solids — consistent. 1,604.17 ÷ 100 = 16.0 ft²/gal (the data sheet gives no coverage figure). One rate for all substrates.Source
• Henry Aqua-Bloc WB (below grade): 80 wet mils, 20 ft²/galMath check: 1,604.17 ÷ 80 = 20.05 — matches.Source
• Prosoco R-Guard Cat 5: Exterior gypsum, OSB, plywood 50–100 ft²/gal; CMU 50–80 ft²/gal; 5 gal; spray or roller; no primerThe page uses 50 ft²/gal, the low end of both ranges, so the gallons are not understated (implied 32.1 wet mils). ICC-ES ESR-3416 calls for a uniform 15 wet mil film (1,604.17 ÷ 15 = 106.9 ft²/gal), thinner than the coverage Prosoco publishes — check with Prosoco for your wall.Source
• Custom RedGard (interior wet areas): Waterproof membrane 55 ft²/gal (1 gal), 192 ft² (3.5 gal); crack prevention 100 ft²/gal; roll onImplied 29.2 wet mils (1,604.17 ÷ 55). Coverage chart is for estimating; actual coverage varies with the job.Source
• LATICRETE Hydro Ban: Two coats, each at 1 gal per 50 ft² (ICC-ES ESR-2417); cured about 20–30 milsImplied 32.1 wet mils per coat, 64.2 in all = 25 ft²/gal for the system. An older Laticrete sheet gives 17–22 wet mils per coat, which would cover more — the ICC-ES figure is used so gallons are not understated.Source
• Roller or spray loss: Your own % for roller nap and overspray — 0 unless you enter itNone of these data sheets publishes a loss for roller or spray. Published spray transfer-efficiency figures are for spray painting parts, not membranes on walls, so none is assumed here.
• Detail coat and fabric: Length × band width at the detail wet mils (default: the field thickness); fabric rolls = length ÷ roll length, rounded upUse the band width, thickness and fabric your product's details call for (inside and outside corners, sheathing joints, cracks, penetrations). Laps between fabric pieces are not added.