For a small stall, pick the Kohler Rely K-8644 (36 x 34, center drain). For a 4-foot alcove, the Rely K-8639. For a 60-inch alcove, the Rely K-8459, or the heavier Ballast K-1937 with an integral flange.
Plumbing Picks is reader-supported. As an Amazon Associate, we earn from qualifying purchases at no extra cost to you.
This guide compares four Kohler shower bases using Kohler’s own spec sheets.
Kohler shower bases compared (Kohler spec sheets)
On a phone, swipe or scroll the table sideways to see every column.
| Model | Size | Drain | Material | Weight |
|---|---|---|---|---|
| Rely K-8644-0 | 36 x 34 in. | Center | Acrylic | 34 lb |
| Rely K-8639-0 | 48 x 32 in. | Left | Acrylic | 51 lb |
| Rely K-8459-0 | 60 x 32 in. | Left | Acrylic | 62 lb |
| Ballast K-1937-0 | 60 x 32 in. | Left | Resin concrete core, acrylic surface | 128 lb |
A shower base, also called a shower pan or receptor, is the floor of a stall shower. Kohler lists the drain location in each model name, so the first step is matching the base to where the drain pipe already comes up through the subfloor. Each sheet recommends the K-9132 shower drain and tells installers to measure the actual product for rough-in details. The three Rely sheets and the Ballast sheet list the KOHLER Plastic Baths and Receptors Lifetime Limited Warranty or refer to Kohler’s warranty page.
Kohler Rely K-8644: 36 x 34 inches, center drain
Choose the Rely K-8644 for a small square-ish stall with the drain in the middle. Kohler’s spec sheet (resources.kohler.com) lists a 36 by 34-inch acrylic alcove base with a center drain, a low threshold, a molded-in textured floor, a water containment bead in the threshold and a single threshold for alcove installation. It weighs 34 pounds and needs 2-5/8 inches of flat surface for a shower door.
Kohler notes the subfloor must be within 1/2 inch of level, and that this receptor has a front lip to account for when installing a door. On October 15, 2026, the standard new offer sold by Amazon.com showed limited stock with model K-8644-0, white.
Check Kohler Rely K-8644-0 shower base on Amazon →
Kohler Rely K-8639: 48 x 32 inches, left drain
Choose the Rely K-8639 for a 4-foot stall with the drain toward the left end. Kohler’s spec sheet (resources.kohler.com) lists a 48 by 32-inch acrylic alcove base with a left drain, the same low threshold, textured floor and water containment bead as the other Rely bases, a weight of 51 pounds and 2-5/8 inches of flat surface for a door. Kohler says the subfloor must be within 1/2 inch of level.
“Left drain” means the drain sits toward the left end when you face the open side. On October 15, 2026, the standard new offer sold by Amazon.com showed limited stock with model 8639-0, white.
Check Kohler Rely K-8639-0 shower base on Amazon →
Kohler Rely K-8459: 60 x 32 inches, left drain
Choose the Rely K-8459 to replace a standard 5-foot tub with a walk-in shower. Kohler’s spec sheet (resources.kohler.com) lists a 60 by 32-inch acrylic alcove base with a left drain, low threshold, textured floor and water containment bead. The drawing shows a 4-11/16-inch overall height, the drain centered 11-1/4 inches from the left end and 15-1/4 inches from the back edge, a 1-5/8-inch wall flange and a front lip that drops 3-1/2 inches. It weighs 62 pounds.
Kohler says the subfloor must be within 1/2 inch of level and to allow for the front lip when fitting a door. On October 15, 2026, the standard new offer sold by Amazon.com showed limited stock with model K-8459-0, white.
Check Kohler Rely K-8459-0 shower base on Amazon →
Kohler Ballast K-1937: 60 x 32 inches, resin concrete core
Choose the Ballast K-1937 for a heavier 60 by 32-inch base with a flange and a low step-over. Kohler’s spec sheet (resources.kohler.com) lists a resin concrete core with an acrylic surface, one-piece construction, an integral flange that helps keep water from seeping behind the wall, a low step-over height and a left drain. The drawing shows a 3-3/16-inch overall height, the drain 7-1/4 inches from the left end and centered front to back, and a 1-1/4-inch flange. It weighs 128 pounds.
Kohler says to install a shower door with this base, that a door with a bottom track is required, and lists compatible Kohler sliding doors. On October 15, 2026, the standard new offer sold by eFaucets showed limited stock with model K-1937-0, white.
Check Kohler Ballast K-1937-0 shower base on Amazon →
Rely versus Ballast: what the sheets say differs
Material and weight are the biggest split. The Rely bases are acrylic and run from 34 to 62 pounds. The Ballast pairs a resin concrete core with an acrylic surface and weighs 128 pounds at the same 60 by 32-inch size as the Rely K-8459, more than double.
Height and lip differ too. The Rely K-8459 drawing shows a 4-11/16-inch overall height and a front lip that drops 3-1/2 inches, with 2-5/8 inches of flat top for a door. The Ballast drawing shows a 3-3/16-inch overall height and 2 inches of flat surface for a door, and Kohler describes it as a low step-over base.
Door rules differ. Kohler requires a bottom-track shower door on the Ballast and cautions about water damage without one. The Rely sheets list the flat space a door needs and note the front lip, without the same requirement.
Drain position differs on the 60-inch models. The Rely K-8459 puts the drain 11-1/4 inches from the left end; the Ballast puts it 7-1/4 inches from the left end. If you are matching an existing drain pipe, compare those numbers to your floor before you pick.
Colors. The Rely sheets list four color codes; the offers linked here are all white (code 0). Kohler’s sheets give nominal sizes, so measure the alcove and the delivered base before you set it.
Check these before you order
- Drain location. Match left, right or center to the drain pipe under the floor; moving a drain means cutting the subfloor.
- Drain body. Kohler recommends the K-9132 shower drain; budget for it separately.
- Level subfloor. The Rely sheets say within 1/2 inch of level.
- Door. The Ballast needs a door with a bottom track; the Rely bases list the flat space a door needs.
- Weight. The Ballast is 128 pounds; plan two people to carry and set it.
- Size check. Measure the alcove stud to stud; Kohler says to measure the actual product for rough-in details.
Which Kohler shower base should you buy?
Pick by the space and the drain. For a small stall, the Rely K-8644 at 36 by 34 inches with a center drain. For a 4-foot alcove, the Rely K-8639. For a tub-to-shower swap in a 60-inch alcove, the Rely K-8459 is the lighter acrylic choice, and the Ballast K-1937 is the heavier resin concrete option with an integral flange. For other brands and tile-ready pans, see our shower pan guide, and for the drain, our Kohler shower drain guide.
Frequently asked questions
Does a Kohler shower base include the drain?
No. Each sheet recommends the K-9132 shower drain as a separate product.
What does left drain mean on a Kohler shower base?
The drain sits toward the left end when you face the open side of the base.
How heavy is the Kohler Ballast shower base?
128 pounds, per Kohler.
What is the Kohler Rely shower base made of?
Acrylic, per Kohler’s sheets.
Does the Kohler Ballast need a shower door?
Yes. Kohler says a shower door with a bottom track is required.
How we chose
This document-based guide makes no hands-on testing claim. We read and rendered Kohler’s spec sheets for the Rely K-8644, K-8639 and K-8459 and the Ballast K-1937. On October 15, 2026, we checked each linked standard new Amazon offer for model, seller, stock and an add-to-cart button. Read our selection method and about Plumbing Picks.
Primary sources
- Kohler Rely K-8644 spec sheet (resources.kohler.com): 36×34 center, 34 lb.
- Kohler Rely K-8639 spec sheet (resources.kohler.com): 48×32 left, 51 lb.
- Kohler Rely K-8459 spec sheet (resources.kohler.com): 60×32 left, drawing, 62 lb.
- Kohler Ballast K-1937 spec sheet (resources.kohler.com): resin concrete, flange, door required.