What counts as an extra deep soaking tub, and what does it demand?

Q: What counts as an extra deep soaking tub?

There is no code definition. Standard American tubs hold 14–16 in of water, and Kohler already calls 16 in a deep soak. We use 20 in of water and above as extra deep. Depth is measured from the drain to the overflow, not from the floor to the rim.

Q: How many gallons does an extra deep tub hold?

For an oval tub with 20 in of water, our gallons calculator gives 88 gallons at 50 × 26 in inside, 114 at 60 × 28 in and 135 at 66 × 30 in. That is roughly 730 to 1,130 lb of water, before the tub and the bather.

Q: What water heater does an extra deep tub need?

About 77% of the fill comes from the tank at a 104°F bath, so 68 to 104 gallons for the sizes above. Few 40–50 gallon tanks supply that in one go. Check the first-hour rating with a licensed plumber.

Q: Will my floor hold an extra deep stone tub?

Assume it will not without a check. A solid marble tub 60 to 72 in long weighs about 1,750–2,230 lb filled with a bather, or 167–178 psf on its footprint. The design live load for most rooms is 40 psf, so ask a structural engineer.

Last updated November 2026.

Quick answer

Standard water depth: 14–16 in on most US tubs (This Old House); Kohler's 60 × 32 in alcove lists 14 in
Our working line for extra deep: About 20 in of water or more, measured to the overflow
Gallons at 20 in: 88–135 gal for oval tubs from 50 × 26 to 66 × 30 in inside (gallons calculator)
Hot water: About 77% of the fill, so 68–104 gal at 20 in depth
Solid stone, 60 to 72 in long: About 1,750–2,230 lb filled with a bather, 167–178 psf (weight model)

An extra deep soaking tub holds water well past the usual 14–16 in, and we treat about 20 in of water or more as the line. At that depth an oval tub 50 to 66 in long holds 88–135 gallons, needs about 68–104 gallons from the water heater, and loads the floor hard.

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What counts as an extra deep soaking tub?

The label is marketing, so use water depth. This Old House lists 14–16 in as typical for a standard tub, with a range of 12–22 in of water across the market, and notes that soaking models reach 24 in or more of wall height. Kohler calls a 16 in depth a deep soaking experience on its Irvine freestanding model, and its 60 × 32 in Devonshire alcove tub lists 14 in.

We draw the line at about 20 in of water. Below that a bather reclines and the water reaches the chest. Above it the tub is a seated, shoulder-high soak, and the hot-water and floor numbers change. The wall height needed for any given depth is covered in the soaking tub depth guide.

Planning a stone bathtub?

Tell us about the room. We reply within one business day with options, and every quote gives the exact dimensions and weight of the piece.

Is water depth the same as tub height?

No. Maker sheets list water depth separately from overall height because the overflow sits below the rim, and the basin starts above the floor. Kohler's Memoirs 60 × 34 in freestanding bath is 23-3/4 in tall yet lists 17-7/16 in of water depth and 80 gallons. The gap reflects the rim above the overflow plus the base under the basin.

Two details decide how deep you really soak. The first is the overflow height. Kohler lists a slotted overflow among the features that allow deep soaking on its Memoirs and Irvine baths, so the overflow type affects the water line. The second is the bather: a seat or a taller person changes how much of the depth is used. Always ask for the water depth to the overflow in inches, and compare tubs on that number, not on height.

How many gallons does an extra deep tub hold?

Gallons rise with depth in a straight line, so each added inch of water adds about 4–7 gallons on these sizes. The table uses oval tubs, which hold about 13% less than rectangles of the same inside size. For other dimensions, run the gallons calculator.

Inside size (oval)	At 14 in	At 16 in	At 20 in	Water weight at 20 in
50 × 26 in	62 gal	71 gal	88 gal	About 734 lb
60 × 28 in	80 gal	91 gal	114 gal	About 951 lb
66 × 30 in	94 gal	108 gal	135 gal	About 1,126 lb

Source: Pietra Fonte gallons calculator, oval shape factor, 8.34 lb per gallon. Maker listings use their own fill points, so compare like for like.

A real-world check: Kohler lists its 67 × 31-1/2 in Irvine at 82.89 gallons with 16 in of water, and its 72 × 36 in Stargaze at 90 gallons with 15-11/16 in. Those sit close to our 16 in numbers for similar lengths.

What water heater does an extra deep tub need?

A bath at 104°F, mixed from 50°F cold water and a 120°F tank, takes about 77% of its volume from the tank. That makes the 20 in column above a hot-water load of about 68, 88 and 104 gallons. Kohler's own sheets ask for a hot water supply of 70% of the bath capacity or more.

Tank size is the wrong test. Jaspector's sizing guide ranks heaters by first-hour rating and gives 78 gallons for a 50-gallon gas tank and 56 for a 50-gallon electric one. It lists 50–80 gallons of hot water for a soaking tub. So an electric 50-gallon unit may fall short of a 114-gallon fill. Options include a larger tank, a high-recovery or tankless unit, or running the tap while the tank recovers. A licensed plumber should size the system.

Will my floor hold an extra deep stone tub?

Check it before you order. IRC Table R301.5 sets 40 psf for non-sleeping rooms and 30 psf for bedrooms as the design live load. Kohler's acrylic sheets list minimum floor loads of 41 psf for a 60 × 32 in alcove tub and 48.8 psf for the 72 × 36 in Stargaze. Solid stone is in a different range.

Outside size, 22 in tall	Marble, empty	Filled with a bather	Load on footprint
60 × 30 in	1,030 lb	1,750 lb	178 psf
66 × 32 in	1,160 lb	1,980 lb	172 psf
72 × 34 in	1,290 lb	2,230 lb	167 psf

Source: Pietra Fonte weight model (2.5 in walls, 70% fill, 200 lb bather, marble at 168 lb/ft³). Taller walls add stone and water.

Heavy does not mean impossible. A tub set over a bearing wall, extra joists or a slab changes the answer, and that is engineering work. See the stone bathtub weight guide for the method.

How do you get in and out of an extra deep tub?

Wall height is the whole story. Retail guidance for ofuro-style deep tubs with 22–30 in walls is to use a step stool and fit grab bars. Kohler's 46 × 46 in Stillness Soak stands 31-11/16 in tall for a 23-5/8 in depth. For a tall wall, the lowest section is the one you step over, so a freestanding tub with a single low point or a shaped rim helps.

Think about the bather too. Children, older relatives and anyone with a bad knee will find a 28 in wall a climb. If that matters, choose a depth near 18–20 in and a longer tub, and place the tub so there is a firm floor and a grab point beside the entry.

What does an extra deep stone tub cost?

Depth adds stone, carving time and shipping weight, so a taller tub costs more than a standard-height one in the same material. We do not publish prices, and every quote is built to your specification. For the market ranges we track by material, see the marble bathtub cost guide, and for size options start at the bathtub sizes guide.

Sources

Every piece is made to order. Tell us about the room and we reply within one business day.

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