Square, Round or Linear Shower Drain — What Is the Difference, and What Size Drain Does a Shower Need?
Square and round shower drains are both centre drains: the floor slopes to them from four sides, and the grate shape is mostly a matter of looks and how the tile is cut [6]. A linear drain is a long channel along one side, and the whole floor tilts toward it as one flat plane [6][7]. What really differs is underneath: a traditional drain clamps the pan liner between two flanges and lets water out through weep holes; a bonded-flange drain takes a membrane bonded on top [4][5][7]. Florida’s code sets the minimum shower drain outlet at 1½ inches, and a 1½-inch trap for showers with a total flow of 5.7 gpm or less [1][2][4].
What is the difference between a square, round and linear shower drain?
Square and round are two grates for the same kind of drain; a linear drain is a different kind. Oatey, a drain maker, describes a centre square drain as one where water flows by a conventional four-way, compound slope toward the drain, and a linear drain as one where water flows by a single slope toward it [6]. The same Oatey article says its 130 Series tile shower drain, made for tile or marble showers with a shower pan liner, comes in square or round, snap-in or screw-in [6] — the same drain, a different grate.
So between square and round the choice is mostly how it looks with the tile. Oatey points out that square drains are easier to tile around because most tile is square, so the tiler does not have to cut a circular opening [6]. It describes linear drains as suited to large-format tile and solid-surface floors, because one slope gives an uninterrupted floor with fewer grout lines, and as the right choice for curbless showers and wet rooms [6]. It also says centre square drains generally cost less, because they need less material and less work on site [6].
The rest of this page is about the two things the grate does not show: how the waterproofing joins the drain, and how the floor slopes to it.
What is under a shower drain — a clamping ring or a bonded flange?
One of two connections, and it decides how the floor is built. The traditional one is a clamping-ring drain. Florida’s residential code requires a flanged drain wherever a shower has a subpan or lining; the flange sits flush with the subbase, has a clamping ring or other device for a watertight joint between lining and drain, and has weep holes into the drain [4]. The Florida plumbing code says the liner must be securely fastened to the waste outlet at the seepage entrance, making a watertight joint [1].
Oatey’s instructions for its tile shower drain — one maker’s instructions, shown because its parts match the drawing below — build it in this order [5]:
- the drain base is solvent-welded to the drainpipe and fastened down through the four holes in its flange [5]
- a sloped base goes under the waterproofing, ¼ inch per foot, sloped up and away from the top of the drain base but not over it [5]
- the pan liner is laid, cut out to the drain hole, and the weep holes are checked clear of liner material and silicone sealant [5]
- the clamping ring goes on over the liner; with the drain plugged, the floor is filled with water to just below the top of the curb and left at least 4 hours [5]
- the drain barrel threads into the clamping ring so the finished floor will be flush with its top [5]
- pea gravel goes over the weep holes, then a mortar bed at least 1½ inches thick over the liner, leaving room for thinset and tile [5]
The second way is a bonded-flange drain. Schluter’s handbook describes the traditional shower as a “water in/water out” system, in which water soaks into the mortar bed and leaves through the weep holes, and its own as a “sealed” one: a waterproofing membrane goes on top of the mortar bed, is bonded with thin-set mortar to the drain’s flange, and the tile is set directly on the membrane [7]. Florida’s residential code allows a bonded waterproof membrane or a liquid-applied one, meeting ANSI A118.10, in place of a sheet liner [4]. The liner materials and the flood test are covered in our article on what is under your shower floor.
How does the floor slope to a centre drain compared with a linear drain?
To a centre drain the floor slopes in from four sides; to a linear drain it is one plane tilted one way. Oatey calls the first a four-way, compound slope and says a linear drain removes it from the shower pan [6]. Schluter says its KERDI-LINE linear drain accommodates a single-plane slope and large-format tile, and can be installed against a wall or at an intermediate location [7].
The amount of slope is set by code, whichever drain you choose. Florida’s residential code says a shower floor must slope uniformly toward the drain, not less than ¼ inch per foot (2 percent) and not more than ½ inch per foot (4 percent), and that the lining under it is sloped ¼ inch per foot toward the weep holes [4]. The Florida plumbing code gives the same 2-percent pitch for liners [1]. Schluter’s instructions for a mortar base under its linear drain slope the bed ¼ inch per foot, using the drain’s bonding flange and a screed at the far side as guides [7].
Our reading of the two slopes: with four planes, the floor has to fold along the lines from the corners to the drain, which is why big tiles suit a linear drain and a single plane — Oatey makes the same point about large-format tile [6].
What size drain does a shower need?
At least 1½ inches, under the code in force in Florida. The Florida Building Code, Plumbing, §421.3 says waste outlets serving showers must be not less than 1½ inches in diameter, with removable strainers not less than 3 inches in diameter and strainer openings not less than ¼ inch [1]. The residential code, §P2708.2, sets the same 1½-inch minimum outlet for shower drains [4].
The trap size depends on how much water the shower can put out. Table 709.1 of the Florida plumbing code rates a shower by the total flow through its showerheads and body sprays: 5.7 gpm or less takes a 1½-inch trap; more than 5.7 up to 12.3 gpm, a 2-inch trap; more than 12.3 up to 25.8 gpm, a 3-inch trap; more than 25.8 up to 55.6 gpm, a 4-inch trap [2]. The same code caps a showerhead at 2.5 gpm at 80 psi, and counts a hand-held spray as a showerhead [3].
Our reading, from those two tables: a shower with one head, or a head and a hand spray, stays at or below 5.7 gpm, so the code minimum is 1½ inches; a shower with several heads or body sprays should be added up before the drain is chosen. Many drain bodies are sold in larger sizes than the minimum — Schluter, for example, lists its KERDI-DRAIN with 2-inch or 3-inch outlets [7].
Do not confuse the pipe size with the grate size. Oatey lists its square grates as typically 4, 5 or 6 inches [6]; that is the size of the top you see, not of the pipe below it.
What are weep holes in a shower drain, and why must mortar stay off them?
They are small openings in a clamping-ring drain at the level of the liner, and they are the only way out for water that has soaked through the tile. Florida’s residential code requires the drain flange to have weep holes into the drain [4]. Schluter explains why: tile is not waterproof, water works down through the mortar bed to the sloped liner and leaves through the weep holes; if the liner was laid flat or the weep holes become clogged, the mortar bed can stay saturated, which raises the potential for efflorescence and mould inside the floor [7].
That is why the drain maker’s instructions protect them twice. Oatey says to make sure the weep holes are clear of liner material and silicone sealant when the liner is cut out, and to put pea gravel over them before the final mortar goes in, so the mortar does not completely cover them [5].
A bonded-flange drain works differently: Schluter’s membrane sits on top of the mortar bed, so water stops at the membrane instead of soaking the bed [7]. If you already see dark grout near the drain, a musty smell or a stain below the shower, our article on signs of a leaking shower pan goes through how each is checked.
Can I swap a round shower drain grate for a square one?
Sometimes — it depends on the drain body underneath, not on the grate. Some makers sell both shapes for the same drain: Oatey offers its 130 Series in square or round, snap-in or screw-in [6], and Sioux Chief sells a round-to-square strainer and adapter kit among its shower pan drain accessories [8]. Those are one maker’s parts for that maker’s drain, so the drain has to be identified first.
Turning a centre drain into a linear drain is not a grate swap. The floor changes from four slopes to one, so the mortar bed and tile have to be rebuilt — that is our reading of the slope difference [6]. Schluter’s handbook says that where a clamping-ring drain is already installed it must be replaced with the KERDI-LINE linear drain, and that to use its own centre drain the old one is either replaced or converted with an adaptor kit [7].
Which shower drain should I choose?
Pick the floor first, then the grate. Oatey’s comparison comes down to this: a centre square drain for a conventional shower at lower cost, a linear drain for large-format tile, a curbless entry or a wet room [6]. Between square and round, the square grate saves round cuts in square tile [6]; beyond that it is looks.
Whichever you choose, the size of the pipe is set by the flow of the shower [2], the slope by the code [4], and the waterproofing by the drain type — a liner clamped into a flanged drain with clear weep holes, or a membrane bonded to the drain’s flange [4][5][7].
What this means in Indian Shores and across Tampa Bay
Florida uses one statewide building code, and the shower drain numbers on this page come from its 2023 edition, the Plumbing volume and the Residential volume [1][2][3][4].
Both photographs on this page are from a bathroom in Indian Shores: a PVC shower pan liner with a square drain, installed next to the toilet in a gutted bathroom, and a 40-mil PVC liner with the square drain in the framed shower. That is the stage at which the drain type and the slope are decided, before any mortar or tile goes down. If you are planning a shower floor and want the drain chosen before the tile is, call 727-470-7126.
Tell us the shower size, the tile and whether you want a curb. Kate, our AI voice assistant, answers the phone 24/7 and takes the request; overnight requests are reviewed first thing in the morning, and site work is Monday to Friday, 8am to 6pm. We speak English and Russian.
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Is a linear shower drain better than a square drain?
Not better — different. Oatey describes a linear drain as suited to large-format tile, curbless showers and wet rooms, and a centre square drain as the lower-cost choice for a conventional shower [6].
What size drain pipe do I need for a shower?
The Florida code minimum is a 1½-inch outlet [1][4]. The trap goes up with the total flow of the heads and body sprays: 1½ inches up to 5.7 gpm, 2 inches up to 12.3 gpm, 3 inches up to 25.8 gpm and 4 inches up to 55.6 gpm [2].
Does a shower drain have to be 2 inches in Florida?
Not by the code minimum: Florida’s plumbing and residential codes both set 1½ inches for a shower drain outlet [1][4]. A 2-inch trap is required once the shower’s total flow is over 5.7 gpm [2].
Can I change a round shower drain cover to a square one?
If the maker of your drain sells a square grate or an adapter for it, yes — Oatey offers its tile shower drain in both shapes [6], and Sioux Chief sells a round-to-square kit for its drains [8]. Identify the drain first.
What are the weep holes in a shower drain for?
They let water that has soaked through the tile and mortar drain off the liner into the pipe. Florida’s residential code requires them [4]; Oatey says to keep them clear and cover them with pea gravel before the mortar goes in [5].
Does a linear drain need a different floor slope?
The same amount, a different shape: one plane tilted toward the drain instead of four [6][7]. The code range is ¼ to ½ inch per foot toward the drain [4].
Do I need a linear drain for a curbless shower?
Oatey calls a linear drain the right choice for curbless showers and wet rooms, because one slope leaves no barrier to step over [6].
Sources
We review and cite. We do not reproduce a paper or a manual — follow the links for the originals.
- [1]Florida Building Code, Plumbing, 8th Edition (2023) — §421.3 Shower waste outlet and §421.5.2 Shower lining — Florida Building Commission / International Code Council · 2023Law / code · §421.3: waste outlets serving showers not less than 1½ in (38 mm) in diameter, removable strainers not less than 3 in in diameter, strainer openings not less than ¼ in; §421.5.2: liners pitched ¼ in per 12 in (2 %) toward the fixture drains, securely fastened to the waste outlet at the seepage entrance making a watertight joint, turned up at least 2 in above the finished threshold. The ICC page returned 403; text read on UpCodes (https://up.codes/viewer/florida/fl-plumbing-code-2023/chapter/4/fixtures-faucets-and-fixture-fittings); read 2026-11-09
- [2]Florida Building Code, Plumbing, 8th Edition (2023) — Table 709.1 Drainage fixture units for fixtures and groups — Florida Building Commission / International Code Council · 2023Law / code · shower (based on the total flow rate through showerheads and body sprays): 5.7 gpm or less — 2 DFU, 1½ in trap; >5.7 to 12.3 gpm — 3 DFU, 2 in; >12.3 to 25.8 gpm — 5 DFU, 3 in; >25.8 to 55.6 gpm — 6 DFU, 4 in. Text read on UpCodes (https://up.codes/viewer/florida/fl-plumbing-code-2023/chapter/7/sanitary-drainage); read 2026-11-09
- [3]Florida Building Code, Plumbing, 8th Edition (2023) — Table 604.4 Maximum flow rates — Florida Building Commission / International Code Council · 2023Law / code · shower head: 2.5 gpm at 80 psi; footnote a: a hand-held shower spray is a shower head. Text read on UpCodes (https://up.codes/viewer/florida/fl-plumbing-code-2023/chapter/6/water-supply-and-distribution); read 2026-11-09
- [4]Florida Building Code, Residential, 8th Edition (2023) — §P2708 Showers and §P2709 Shower receptors — Florida Building Commission / International Code Council · 2023Law / code · P2708.2: shower drains outlet not less than 1½ in; P2709.1: finished floor slopes uniformly toward the drain not less than ¼ and not more than ½ unit vertical in 12 (2–4 %), floor drains flanged for a watertight joint; P2709.2: lining of sheet lead, sheet copper, PVC (ASTM D4551) or CPE (ASTM D4068), hot mopping, or bonded / liquid-type membrane to ANSI A118.10; P2709.3: lining sloped ¼ in per 12 in to the weep holes in the subdrain; P2709.4: approved flanged drain with subpans or linings, flange flush with the subbase with a clamping ring or other device for a watertight connection, flange to have weep holes into the drain. Text read on UpCodes (https://up.codes/viewer/florida/fl-residential-code-2023/chapter/27/fixtures); read 2026-11-09
- [5]Instruction Guide — Tile Shower Drains (application with wood subfloor; application with concrete slab subfloor) — Oatey Co. · 2023Manufacturer's manual · parts: strainer, adjustable drain barrel, reversible clamping ring, collar bolts, drain base; drain base solvent-welded and fastened through four countersunk holes; test plug rated to 40 ft of head; sloped base ¼ in per ft up to but not over the drain base; liner cut to the drain hole, weep holes clear of liner material and silicone; inverted ring raises the floor about ¾ in; flood test with water just below the top of the curb, minimum 4 hours; barrel threaded into the ring flush with the finished floor; pea gravel over the weep holes so the mortar does not completely cover them; minimum 1½ in mortar bed over the liner. One maker’s instructions, © 2023, Oatey-branded PDF on Oatey’s asset host; read 2026-11-09
- [6]Linear vs. center square drains: Five considerations to drive your choice — Oatey Co. · 2022Manufacturer's manual · manufacturer’s article, 2022-05-05: centre square drain — conventional four-way compound slope; linear — single slope, removes the four-way slope; linear suits large-format tile and solid surface, curbless and wet rooms; square easier to tile around, no circular cut; centre square drains generally cost less (less material and on-site work); 130 Series for tile or marble showers with a pan liner, in square or round, snap-in or screw-in; square drains typically 4, 5 or 6 in; read 2026-11-09
- [7]Schluter-Shower System Installation Handbook (04/2023, doc. 552420) — Schluter Systems L.P. · 2023Manufacturer's manual · traditional system is “water in/water out”: pre-slope to the weep holes, liner clamped into the drain, second mortar bed; tile is not waterproof; mortar bed can stay saturated if the pre-slope is ignored or the weep holes clog, raising the potential for efflorescence and mould; Schluter system is “sealed”: KERDI membrane bonded with thin-set to the drain’s bonding flange, tile set on it; KERDI-DRAIN square grates, 2 in or 3 in outlets, adaptor kits convert an existing clamping-ring drain; KERDI-LINE single-plane slope, large-format tile, against walls or at intermediate locations; mortar base sloped ¼ in per 12 in using the bonding flange and a perimeter screed; an installed clamping-ring drain must be replaced with KERDI-LINE. One maker’s instructions, not necessarily the brand we install; Schluter’s own handbook, copy hosted by a retailer; read 2026-11-09
- [8]821-2QAS Round-to-Square Strainer & Adapter Kit — Sioux Chief Manufacturing · 2026Manufacturer's manual · product page: “Round-to-Square Strainer & Adapter Kit”, stainless steel square strainer, listed under shower pan drain accessories; the page does not list which drains it fits; one maker’s part; read 2026-11-09
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