How to Use the Waterproofing Material Calculator
Planning a DIY waterproofing project means knowing how much coating to buy before you head to the store. This calculator multiplies your area (ft²) by the number of coats and divides by the coverage rate for your chosen coating type to get the total gallons needed, plus how many 5-gallon buckets that works out to.
The formula is: gallons needed = (area in ft² × number of coats) ÷ coverage rate (sqft/gal). For example, a 200 ft² roof coated twice with an elastomeric coating (100 sqft/gal) needs about 4 gallons — just under one 5-gallon bucket.
Coverage rates vary by coating type. Elastomeric roof coatings spread the thinnest and stretch further per gallon, acrylic waterproof coatings sit in the middle, and thicker deck or foundation coatings designed for heavier wear use noticeably more material per square foot. Rough or textured surfaces, plus normal roller and brush application loss, mean it's smart to buy 10-15% more than the calculated amount.
Before applying, clear away dirt and debris and seal any cracks first — surface prep has a big impact on how well the coating performs long-term. Applying several thin, even coats holds up better against cracking than one thick coat. Coating in mild, dry weather (spring or fall rather than right before rainy season) gives each coat enough time to cure properly.
Frequently Asked Questions
Most waterproof coatings recommend 2-3 coats for even thickness and reliable coverage. Let each coat dry fully before applying the next.
Yes, buying 10-15% more than the calculated amount is recommended to account for uneven surfaces and roller or brush application loss.