Shower Pan Size Calculator
Finished inside size
IRC P2708.1
Meets code
- Floor area
- 1,728 sq in · 12 sq ft
- Smallest dimension
- 36 in (min 30)
- Rise to the walls (1/4 in/ft)
- 0.5 in
- Rise to the corners
- 0.63 in
Measured inside the finished walls, clear of valves and grab bars. Local codes may differ.
Tools the pros use for this job
Tile-Ready Shower Pan Kit
VEVOR Shower Curb Kit, 38"x60" Watertight Shower Curb Overlay with 4" PVC Central Bonding Flange, 4" Stainless Steel Grate, 2 Cuttable Shower Curb and Trowel, Shower Pan Slope Sticks Fit for Bathroom
$171.90
Check price on AmazonA pre-sloped foam tray replaces the mortar bed.
Linear Shower Drain
One-way slope lets you use large tile on the floor.
Shower Pan Liner
For a traditional mortar-bed pan.
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Common shower pan sizes checked
| Size | Area | IRC P2708.1 | Rise to wall (center drain) |
|---|---|---|---|
| 32 × 32 in | 1,024 sq in (7.1 sq ft) | Meets | 0.33 in |
| 36 × 36 in | 1,296 sq in (9 sq ft) | Meets | 0.38 in |
| 42 × 36 in | 1,512 sq in (10.5 sq ft) | Meets | 0.44 in |
| 48 × 32 in | 1,536 sq in (10.7 sq ft) | Meets | 0.5 in |
| 48 × 36 in | 1,728 sq in (12 sq ft) | Meets | 0.5 in |
| 60 × 30 in | 1,800 sq in (12.5 sq ft) | Meets | 0.63 in |
| 60 × 32 in | 1,920 sq in (13.3 sq ft) | Meets | 0.63 in |
| 60 × 36 in | 2,160 sq in (15 sq ft) | Meets | 0.63 in |
Sizes are nominal outside dimensions of bases on the market; the code measures the finished inside, so check the maker's drawing — the inside of a base, or of a tiled shower after backer board and tile, is smaller. Local codes may amend the IRC.
Do this math on the job site — in the free app
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How this calculator works
Code size. IRC P2708.1 requires at least 900 sq in of floor inside the finished shower and at least 30 in in its smallest dimension, measured from finished wall to finished wall, clear of valves, heads, soap dishes and grab bars. The exception allows a 25 in minimum dimension when the area is at least 1,300 sq in.
Slope. IRC P2709.1 slopes a shower floor 0.25 in to 0.5 in per foot toward the drain. At the minimum, the floor at the wall sits 0.25 in higher than the drain for every foot of run: half the longer side for a center drain (more at the corners), the full depth for a linear drain at the back wall.
Worked example. A 36 × 36 in shower is 1,296 sq in with a 36 in minimum dimension, so it passes. With a center drain the floor rises 18 in ÷ 12 × 1/4 = 0.375 in to the walls and about 0.53 in to the corners. A 32 × 28 in shower (896 sq in, 28 in) fails both tests.
Frequently asked questions
What is the minimum shower size?
Under IRC P2708.1, 900 sq in of floor and at least 30 in in the smallest direction, measured inside the finished walls — a 30 × 30 in shower is the smallest square that passes. A narrower shower is allowed down to 25 in if the area is 1,300 sq in or more.
What are standard shower pan sizes?
Bases are commonly sold in sizes such as 32 × 32, 36 × 36, 48 × 32, 48 × 36 and 60 × 30, 60 × 32 or 60 × 36 in for alcove showers that replace a tub. Measure your rough opening and check the maker's inside dimensions against the code minimum.
Is a 32 × 32 shower to code?
Usually, if the finished inside is at least 30 in each way: 30 × 30 in is 900 sq in, exactly the minimum. Check the base's inside dimension — some 32 in bases leave less than 30 in inside once walls and trim are finished.
How much slope does a shower pan need?
IRC P2709.1 calls for 0.25 in to 0.5 in per foot toward the drain. A 48 × 36 in pan with a center drain rises at least 0.5 in from the drain to the side walls.
How do I measure for a shower pan?
Measure the rough opening between studs at the floor in both directions, and the drain's distance from the walls. Buy a base sized for the opening, or for a tiled pan, subtract backer board and tile thickness to get the finished inside size and check it here.
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