RedGard Calculator
Your shower
RedGard to buy
2 × 1 gal
- Gallons needed
- 1.58 gal
- Wall area (55 sq ft/gal)
- 66 sq ft
- Floor as pan liner (40 sq ft/gal)
- 15 sq ft
- Coats
- 2, second at right angles
- Dry time per coat
- 1–1.5 h (up to 12 h)
Gallons are rounded up to whole pails: 2 gal bought.
Tools the pros use for this job
RedGard Waterproofing Membrane
RedGard Waterproofing Membrane
Ready to use; two coats waterproof a shower in an afternoon.
Check price on AmazonReady to use; two coats waterproof a shower in an afternoon.
Fiberglass Mesh for Corners
Embedded at changes of plane and over board seams.
Wet Film Thickness Gauge
Check each coat stays under 40 mils wet.
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Prices as of Oct 1, 2026, 4:37 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
RedGard coverage chart
| Use | 1 gal | 3.5 gal |
|---|---|---|
| Crack prevention | 100 sq ft | 350 sq ft |
| Waterproof membrane (ANSI A118.10) | 55 sq ft | 193 sq ft |
| IAPMO shower pan liner | 40 sq ft | 140 sq ft |
| Crack isolation (ANSI A118.12) | 25 sq ft | 88 sq ft |
Custom Building Products, RedGard TDS-104 (the sheet rounds the 3.5 gal figures). The chart is for estimating; coverage varies with the surface and how it is applied.
RedGard for common showers
| Alcove, 6 ft walls | Walls only | Walls + floor pan |
|---|---|---|
| 3 × 3 ft | 0.98 gal | 1.21 gal |
| 4 × 3 ft | 1.09 gal | 1.39 gal |
| 5 × 2.5 ft | 1.09 gal | 1.4 gal |
| 5 × 3 ft | 1.2 gal | 1.58 gal |
| 6 × 3 ft | 1.31 gal | 1.76 gal |
Do this math on the job site — in the free app
Smart Tile Calculator for Android: offline, in your pocket, free.
How this calculator works
Area. Wall area is the wall width times the height you waterproof: back wall plus both sides for an alcove, two walls for a corner shower. The floor is width × depth. Add niches, the curb and any bench as extra square feet.
Coverage. RedGard's data sheet (TDS-104) gives, per gallon: 55 sq ft as a waterproof membrane (two coats at 110 sq ft each, ANSI A118.10), 40 sq ft as an IAPMO shower pan liner (two coats at 80), 100 sq ft as crack prevention and 25 sq ft for ANSI A118.12 crack isolation. Walls use the waterproofing rate and a floor coated as the pan liner uses the pan-liner rate.
Pails. RedGard comes in 1 and 3.5 gallon pails. The calculator picks the mix with the fewest gallons left over.
Worked example. A 5 × 3 ft alcove waterproofed 6 ft up, floor as the pan liner: walls (5 + 3 + 3) × 6 = 66 sq ft ÷ 55 = 1.2 gal, floor 15 sq ft ÷ 40 = 0.375 gal, 1.58 gal in all — two 1 gallon pails.
Frequently asked questions
How much RedGard do I need for a shower?
Divide the wall area by 55 sq ft per gallon and, if RedGard is also your pan liner, the floor by 40. A 5 × 3 ft alcove waterproofed 6 ft up has 66 sq ft of wall (1.2 gal) and 15 sq ft of floor (0.38 gal): about 1.6 gallons, so two 1 gallon pails.
How many coats of RedGard?
Two. The data sheet has you apply the second coat at right angles to the first once the first has turned solid red. As a waterproof membrane each coat goes on at about 110 sq ft per gallon; as an IAPMO pan liner, 80.
How long does RedGard take to dry?
Typically 1 to 1.5 hours per coat — it is dry when it turns solid red with no pink — but up to 12 hours in cool or humid conditions. After both coats have cured you can flood test.
How thick should RedGard be?
Thin, even coats: the data sheet says the wet film should never exceed 40 mils in any case. Use the recommended coverage rate per coat rather than building it up in one pass.
Can RedGard be used as a shower pan liner?
Yes — it is listed with IAPMO as a shower pan liner when applied in two coats at 80 sq ft per gallon each (40 sq ft per gallon in total), over a properly sloped mortar bed. Follow the data sheet's details for the drain and curb.
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