Waterproofing Calculator

Enter the floor and wall-band size. Get the area and gallons to coat it.

100% in your browser - no upload, no sign-up.

How to use this waterproofing calculator

1. Enter the floor length and width in feet.
2. Enter how far the membrane runs up the walls (curb, shower walls) and the coverage printed on the product.
3. Read the membrane area and gallons - a waste allowance is included.

How the waterproofing amount is calculated

Wet-area waterproofing covers the floor (length × width) plus the band that runs up the surrounding walls - the perimeter, 2 × (length + width), times the wall-band height. The calculator adds your waste allowance, then divides the total area by the coverage per gallon and rounds up. Coverage depends on the product and the number of coats (two is common), so treat the 50 ft²/gal default as approximate and confirm it on the label.

Frequently asked questions

How much waterproofing do I need for a shower?

Add the floor area to the wall band area (perimeter × how high the membrane runs), then divide by the product's coverage per gallon. A 5 × 8 ft floor with a 6-inch band is about 66 ft²; at 50 ft²/gal for two coats that's roughly 2 gallons. Enter your sizes above.

How far up the wall should waterproofing go?

For a standard bathroom floor, a few inches up the wall (a curb) is typical; for a shower, run it the full height of the wet wall - often 6 ft or more. Set the wall-band height to match, and follow your local code and the membrane's instructions.

Why is the coverage just an estimate?

Liquid membranes differ, and you usually apply two coats, so real coverage per gallon varies widely by brand. This tool defaults to a typical figure but lets you enter your product's number - always check the label before buying.