Shower Waterproofing Calculator
Membrane and drain system for tile shower installations.
About this calculator
Total Membrane Area scales directly with Waterproofed Wall Height, Shower Length, and Shower Width, but Number of Walls is the input a small nudge won't reveal: it's a coded 1-4 selector whose default of 3 rounds right back to 3 under a +/-10% probe. Full range shows a real effect though -- at this calculator's other defaults, waterproofing only 1 wall needs about 40 sq ft of membrane, while all 4 walls needs about 125 sq ft, roughly 3x more, since Wall Area scales directly with how many of the shower's sides you're covering. Membrane Type is a genuine either/or choice, not a size adjustment: Liquid-Applied (type 1) and Sheet Membrane (type 2) cover the exact same square footage, but Material Needed is reported in different units for each -- gallons for liquid, rolls for sheet -- so "2" gallons and "1" roll aren't directly comparable numbers even though they describe the same 97 sq ft job.
At this calculator's defaults the two methods land close in cost (about $128 liquid vs. $133 sheet), with liquid-applied actually the cheaper of the two here despite needing a higher material-count number.
Inputs
Results
Total membrane area (sq ft)
97
How to Use This Calculator
- Enter Shower Length (ft) and Shower Width (ft) — the interior dimensions of the shower enclosure.
- Set Waterproofed Wall Height (ft): standard showers require at least 6 ft, steam showers require full ceiling height.
- Enter Number of Walls to waterproof (3 for alcove showers, 4 for freestanding).
- Select Membrane Type (1=liquid-applied such as RedGard, 2=sheet membrane such as Schluter Kerdi).
- Review Total Membrane Area (sq ft) and Material Needed (gallons or rolls) for your product order.
- Check Seam Tape (linear ft) and Tape Rolls for corners and transitions, and Estimated Material Cost for budgeting.
How the result changes with Waterproofed wall height (ft)
| Waterproofed wall height (ft) | Total membrane area (sq ft) |
|---|---|
| 4 | 55.9 |
| 6 | 76.5 |
| 12 | 138.1 |
What each input means
- Shower length (ft)
- Interior length of the shower enclosure in feet.
- Shower width (ft)
- Interior width of the shower enclosure in feet.
- Waterproofed wall height (ft)
- Height to waterproof on walls. Industry standard is full height (ceiling) for steam showers, or at least 6 ft for standard showers.
- Number of walls
- Number of shower walls to waterproof (3 for alcove, 4 for freestanding).
- Membrane type (1=liquid, 2=sheet)
- 1 = liquid-applied (RedGard, HydroDefense) at ~57 sq ft/gal. 2 = sheet membrane (Kerdi) at ~108 sq ft/roll.
- Seam overlap (inches)
- Overlap at seams per manufacturer specs. Typically 2 inches for sheet membrane.
What each result means
- Total membrane area (sq ft)
- Total area to waterproof including 10% waste factor.
- Floor/pan area (sq ft)
- Shower floor area requiring waterproofing.
- Wall area (sq ft)
- Total wall area to be waterproofed.
- Material needed (gallons or rolls)
- Gallons of liquid membrane or rolls of sheet membrane required.
- Seam tape needed (linear ft)
- Linear feet of seam/transition tape for corners and seams.
- Tape rolls needed
- Number of 33 ft seam tape rolls to purchase.
- Estimated material cost ($)
- Approximate material cost based on average pricing.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersShower length (ft) = 3, Shower width (ft) = 3, Waterproofed wall height (ft) = 8, Number of walls = 3 = 6 input(s) provided
- Calculate Total membrane areaTotal membrane area = totalMembraneArea * 1.1097 = 97
- Calculate Floor/pan areaFloor/pan area = showerLength * showerWidth9 = 9
- Calculate Wall areaWall area = avgWallLength * numWalls * wallHeight72 = 72
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Does the number of walls I'm waterproofing really change the material needed by that much?
Yes. Number of Walls is a coded 1-4 selector, so a small nudge around its default of 3 won't show any change, but picking a genuinely different count does: at this calculator's other defaults, 1 wall needs about 40 sq ft of membrane while all 4 walls needs about 125 sq ft -- roughly 3x more.
Is Sheet Membrane always cheaper or more expensive than Liquid-Applied?
At this calculator's defaults (a 3x3 ft shower, 8 ft walls, 3 walls), Liquid-Applied comes out slightly cheaper -- about $128 versus $133 for Sheet Membrane -- but both cover the exact same total membrane area. The Material Needed numbers (2 gallons vs. 1 roll) aren't directly comparable since they're different units, not a size difference.
Why does Material Needed show such a small number for sheet membrane compared to liquid?
Because the units are different, not because sheet membrane covers less area. Sheet membrane rolls cover about 108 sq ft each, while liquid-applied membrane covers about 57 sq ft per gallon, so the same total membrane area needs fewer rolls than gallons -- it's a unit-size difference, not a coverage difference.
Does Membrane Type change the shower's Wall Area or Floor Area?
No. Wall Area and Floor/Pan Area are set purely by Shower Length, Shower Width, Waterproofed Wall Height, and Number of Walls -- Membrane Type only determines which product covers that area and how the material quantity and cost are calculated, not the area itself.
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