Shower Waterproofing Calculator: Membrane, Tile, Thinset and Grout

What the shower calculator adds up

A shower is three jobs on the same few square feet: waterproofing the pan and walls, setting tile on them, and grouting it. Each one is measured a little differently, which is why one number for "the shower" is rarely right.

• Floor: length x depth. It is tiled, waterproofed, set in thinset and grouted.
• Tiled walls: the wall run (back wall plus both side walls for an alcove, back plus one side for a corner shower) times the tile height.
• Membrane: the floor plus the wall run times the waterproofing height, which can be lower or higher than the tile.

Waste is added to every area. Tile is counted per surface because the floor and walls usually use different tiles. Thinset is worked out per surface at its own trowel notch, then the two are added before rounding up to whole bags, so you do not buy an extra bag twice. Grout is done the same way, with each surface's tile size and joint width, because a mosaic floor uses several times more grout per square foot than large wall tile.

Worked example: 5 x 3 ft alcove shower

Walls tiled and waterproofed to 7 ft, 2 x 2 in mosaic on the floor, 12 x 24 in tile on the walls, 1/8 in joints, 10% extra. The floor is 15 sq ft, the tiled walls 77 sq ft and the membrane area 92 sq ft.

• Tile: 527 mosaic pieces for the floor and 42 wall tiles.
• Membrane: 1 × 3.5 gal pail of Custom RedGard (about 2.5 gal) or 3 × 1 gal pails of LATICRETE HYDRO BAN (about 2 gal). Fewest containers: 1 × 3.5 gal pail of Custom RedGard Waterproofing and Crack Prevention Membrane.
• Thinset: with a 1/4 x 1/4 in notch on the floor and 1/4 x 3/8 in on the walls, 2 bags (50 lb) of Custom VersaBond-LHT (about 1.6 bags, 100 lb in all). Fewest bags: 2 bags (40 lb) of ARDEX X 77 MICROTEC.
• Grout: 1 × 25 lb (11.34 kg) bag of Custom Polyblend Plus (about 0.36 bags); fewest packages 1 × 1 gal unit of Custom CEG-Lite.

A 4 x 4 ft corner shower with the same tile and heights has two tiled walls instead of three: 56 sq ft of wall and 72 sq ft of membrane, which is 2 × 1 gal pails of RedGard.

Things the calculator leaves to you

Curbs, benches, niches and the ceiling of a steam shower are extra surfaces; add their area to the length or raise the waste figure. Membranes need extra passes or fabric at corners, seams, drains and valve openings, which the data sheet coverage does not include. Large wall tile, such as 12 x 24 in and up, is often set with a 1/2 x 1/2 in notch for full coverage, which roughly halves how far a bag of thinset goes; pick that notch in the wall trowel menu if that is your plan. ARDEX 8+9 is calculated at its rate over drywall or backer board; over a concrete or mortar bed its data sheet gives a lower rate, shown on its product page.

Compare one material in depth

Each part of this page has its own calculator with more options: the waterproofing calculator (every application each membrane lists), the tile calculator (boxes, layouts and waste), the thinset coverage calculator and the grout calculator. The thinset coverage chart and grout coverage chart show every product side by side.

FAQ

How much RedGard do I need for a shower?

For a 5 x 3 ft alcove shower waterproofed to 7 ft, the floor is 15 sq ft and the three walls are (5 + 3 + 3) x 7 = 77 sq ft, so 92 sq ft in all. With 10% extra and Custom's shower pan rate of two coats at 80 sq ft per gallon per coat, that is about 2.5 gallons: 1 × 3.5 gal pail. A 6 x 3 ft shower waterproofed to 8 ft comes to about 3.1 gallons (1 × 3.5 gal pail).

How many square feet does a gallon of shower waterproofing cover?

Per finished membrane, roughly 40 to 50 sq ft for most liquid membranes once both coats are on: Custom RedGard 2 coats at 80 sq ft per gallon per coat (40 finished), LATICRETE HYDRO BAN 2 coats at about 100 (50 finished), MAPEI Mapelastic AquaDefense about 60 finished per gallon by its packaging table. Each figure is the manufacturer's own; the calculator uses them as printed.

How high should I waterproof shower walls?

Waterproof every surface the shower will wet. Many installers take the membrane to the top of the tile or at least above the shower head; the calculator lets you set the waterproofing height separately from the tile height. Follow the membrane's instructions and local code, and remember the curb, bench and niche faces, which this calculator does not include.

How many tiles do I need for a shower?

With the defaults (5 x 3 ft alcove, walls tiled to 7 ft, 1/8 in joints, 10% extra), the floor takes 527 two-inch mosaic tiles and the walls 42 tiles of 12 x 24 in. Mosaics are sold in sheets, usually about 1 sq ft each, so for the floor buy sheets to cover 16.5 sq ft. The tile calculator turns tile counts into boxes.

Why are some membranes missing from the list?

Only membranes whose data sheet lists ANSI A118.10 waterproofing are included. Crack isolation membranes such as MAPEI Mapelastic CI meet ANSI A118.12 only and are not meant to waterproof a shower, so they are left out even though their coverage looks similar.

Sources

Coverage for every membrane, mortar and grout comes from the manufacturer's data sheet named on its product page. Tile counts are geometry: each tile with its share of the joint covers (length + joint) x (width + joint).