Minimum shower size and tub layout checker
Under the 2021 IRC a shower needs at least 900 square inches inside, with no side under 30 inches, a door at least 22 inches clear and 24 inches of floor in front. A 30 x 30 inch shower is the legal minimum; NKBA recommends 36 x 36. A narrower 25 inch shower passes only with 1,300 square inches.
Updated · By the Interior Redesign AI editorial team · Sources cited on the page
Measure inside the finished tile or panels, not the framing. Valves, shower heads, soap dishes and grab bars don't count against the size.
IRC shower size check
Meets code
1,024 sq in inside, smallest side 32 in. Code minimum 900 sq in with no side under 30 in.
- OK32 × 32 in = 1,024 sq in, with no side under 30 in: meets IRC P2708.1.
- OKA 24 in opening meets the 22 in minimum clear width (P2708.1.1).
- OK30 in in front of the opening meets the IRC 24 in and NKBA's 30 in.
- CheckUnder NKBA's recommended 36 × 36 in interior. Legal, but tight for most adults.
Code checks use the 2021 IRC (P2708.1, P2708.1.1, Figure R307.1); NKBA lines are design advice. Hinged shower doors must open outward. Some states use the Uniform Plumbing Code instead, with different shower rules, so confirm with your building department.
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Key numbers
- Shower floor area (IRC P2708.1)
- At least 900 sq in, measured inside the finished walls
- Smallest side (IRC P2708.1)
- 30 in, or 25 in if the area is at least 1,300 sq in (exception 2)
- Door or opening (IRC P2708.1.1, P2708.1)
- At least 22 in clear finished width; hinged doors open outward (P2708.1)
- In front of the opening (IRC Figure R307.1)
- 24 in clear
- NKBA recommended shower
- 36 × 36 in interior, 30 in clear in front of every fixture
- Standard alcove tub
- 60 in long, 30-32 in wide, 14-16 in deep
- Wall finish (IRC R307.2)
- Nonabsorbent to at least 6 ft above the floor in showers and over tubs with shower heads
Worked example
A 32 × 32 in corner shower
Finished interior 32 × 32 in, a 24 in hinged door, 28 in of floor in front of it.
- Area: 32 × 32 = 1,024 sq in, over 900, and no side under 30 in: meets P2708.1.
- Opening: 24 in is at least 22 in: meets P2708.1.1.
- Front: 28 in meets the IRC's 24 in but is under NKBA's 30 in.
- Size: under NKBA's recommended 36 × 36 in.
It passes the 2021 IRC; NKBA would want 2 more in of floor in front and a 36 in square shower.
How we calculate
For a shower we multiply the finished interior width by depth and compare it with the 2021 IRC (P2708.1): at least 900 square inches with no side under 30 inches, or the second exception, no side under 25 inches with at least 1,300 square inches. Valves, shower heads, soap dishes and grab bars do not count against the size, and the code measures at threshold height up to 70 inches above the drain.
The opening must be at least 22 inches clear (P2708.1.1) and Figure R307.1 shows 24 inches clear in front of it. NKBA's Bathroom Planning Guidelines recommend 36 × 36 inches inside and 30 inches in front; those lines are advice, so they show as a check, not a failure.
For a tub we check that it fits the alcove wall to wall and has NKBA's 30 inches in front. The 2021 IRC's 21 inch front clearance in P2705.1 names toilets, lavatories and bidets, not tubs, so we do not apply it to the tub.
Estimates, sources
Planning estimates and published guidelines, not quotes, designs or code rulings. Figures were checked on each source on the date shown. Local prices, your home and your jurisdiction's adopted code decide the real answer.
- 2021 International Residential Code, Chapter 27 Plumbing Fixtures (P2705.1, P2708.1) (International Code Council (ICC), as of Oct 26, 2026): P2705.1 item 5: a water closet, lavatory or bidet not closer than 15 in from its center to any side wall, partition or vanity, or 30 in center-to-center between adjacent fixtures; at least 21 in clearance in front of a water closet, lavatory or bidet. P2708.1: shower at least 900 sq in, at least 30 in minimum finished interior dimension, measured at threshold height up to 70 in above the drain; hinged shower doors open outward; exception 2: 25 in minimum dimension if the area is at least 1,300 sq in. P2708.1.1: access opening at least 22 in clear finished width
- 2021 International Residential Code, Chapter 3 (R303.3, R307.1, Figure R307.1, R307.2) (International Code Council (ICC), as of Oct 26, 2026): Figure R307.1: 15 in from toilet centerline to a side wall, 21 in clearance in front of the toilet and lavatory, 24 in clearance in front of the shower opening, 30 in shower minimum; R307.2: walls above tubs with shower heads and in showers finished with a nonabsorbent surface to at least 6 ft above the floor; R303.3: a bathroom needs 3 sq ft of window (half openable) unless it has artificial light and a local exhaust system sized per M1505
- Bathroom Planning Guidelines with Access Standards (National Kitchen & Bath Association (NKBA), as of Oct 26, 2026): recommended: 30 in clear floor space in front of every fixture; 18 in from toilet or bidet centerline to any fixture, wall or obstacle; 20 in from lavatory centerline to a side wall; 36 in between two lavatory centerlines; shower interior at least 36 x 36 in; lavatory height 32-43 in; 32 in clear door opening (code references based on the 2015 IRC)
- Standard Bathtub Sizes (This Old House, as of Oct 26, 2026): most standard alcove tubs measure 60 in long, 30-32 in wide and 14-16 in deep (updated 06/05/2026)
Common shower sizes against the code
A narrow shower can still pass on area: a 28 × 48 in shower passes through exception 2: no side under 25 in and 1,344 sq in, over 1,300. A 24 in wide shower fails at any length, because the exception still needs 25 in.
| Shower | Area | IRC | NKBA 36 × 36 |
|---|---|---|---|
| 30 × 30 in | 900 sq in | Meets | No |
| 32 × 32 in | 1,024 sq in | Meets | No |
| 36 × 36 in | 1,296 sq in | Meets | Yes |
| 30 × 48 in | 1,440 sq in | Meets | No |
| 28 × 48 in | 1,344 sq in | Meets (exception 2) | No |
| 24 × 60 in | 1,440 sq in | Fails | No |
Tub alcoves
Most alcove tubs are 60 in long and 30-32 in wide, sized to fit a 5 ft alcove wall to wall. A 60 × 30 in tub in a 60 × 32 in alcove fits, with 2 in of depth left over.
If the alcove is longer than the tub, plan a wall build-out at one end; an alcove tub's flanges need to meet the walls on three sides. Over a tub with a shower head, the IRC (R307.2) needs a nonabsorbent wall finish to at least 6 ft above the floor.
How to use this tool
Pick shower or tub
Check a shower stall, or a bathtub in its alcove.
Measure the finished inside
Inside the tile or panels, not the framing: width, depth and the door's clear opening.
Measure in front
Clear floor from the opening to the nearest wall, vanity or toilet.
Read each line
OK, check or fix for every code minimum and NKBA recommendation.
Questions
What is the minimum shower size by code?
Under the 2021 IRC, 900 sq in of finished interior with no side under 30 in, so 30 × 30 in is the smallest square shower. A shower with a 25 in side is allowed if it has at least 1,300 sq in.
What is the minimum shower door width?
The 2021 IRC (P2708.1.1) requires a clear, unobstructed finished opening of at least 22 in, and P2708.1 requires hinged shower doors to open outward. Check your local code for amendments.
How much space do you need in front of a shower?
Figure R307.1 of the 2021 IRC shows 24 in clear in front of the shower opening. NKBA recommends 30 in in front of every bath fixture.
Is a 32 x 32 shower big enough?
It meets the code with room to spare (1,024 sq in), but NKBA recommends 36 × 36 in for comfort. A 32 in shower suits a small bath; test it by standing in a taped-out square.
Can a shower be 30 x 48 inches?
Yes. 30 × 48 in is 1,440 sq in with no side under 30 in, so it meets P2708.1. It falls short of NKBA's 36 in recommended minimum side.
What size is a standard bathtub?
Most alcove tubs are 60 in long, 30 to 32 in wide and 14 to 16 in deep. Freestanding and soaking tubs vary much more.
Does my city use these rules?
Only if it adopted the 2021 IRC without changes. Some states use the Uniform Plumbing Code, which words the shower rules differently, so confirm with your building department.
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