What size chest freezer for a cold plunge?

Interior volume is the conversion applied to the freezer’s own rated capacity. Usable water is that volume at 70%, which is our stated assumption for filling to shoulder depth with a body displacing water — not a published figure. If you fill shallower, scale it down; the point of stating the assumption is that you can change it.

1. Interior depth, before anything else. This is the spec that decides whether the build works, and it is the one capacity ratings hide completely. You need enough depth that the water comes up over your shoulders when you are sitting or kneeling in it, because a plunge that leaves your upper back in the air is a leg bath. Two cabinets with identical cubic foot ratings can differ by several inches of depth. Measure it, or get it in writing.

2. Interior length, second.Depth decides how much of you is submerged; length decides whether you can sit at all. Work out how you intend to sit — legs folded, knees up, cross-legged — and check that against the floor of the cabinet rather than its volume. This is the measurement most people take after delivery, which is the expensive order to take it in.

3. Then the volume, and smaller than you think.Once depth and length work, less water is strictly better. Every gallon has to be chilled down once and then held against heat leaking in, forever, and that is your monthly cost rather than a one-off. A chest freezer already has thicker insulated walls than almost any purpose-built tub, which is precisely why this conversion is cheap to run — do not throw that advantage away by buying a cabinet twice the size you need. The same logic drives our best-value tub rankings.

4. Then whether it is a chest or an upright. It has to be a chest freezer, not an upright. A chest cabinet opens upward and holds water in a basin; an upright has a door on the front and will empty itself across your floor. This sounds obvious written down and is a genuinely common mistake when people shop by price and cubic feet on a listing page.

5. Then accept what you are doing.A chest freezer is a food appliance, and holding standing water in one is outside every manufacturer’s intended use, warranty and electrical assumptions. That is why we do not compare freezer models or point you at one — recommending a specific unit would imply an approval that does not exist. Read our conversion guide and the GFCI guide before you start, and treat the electrical side as the part not to improvise on.

6. Finally, size the water care to the usable gallons. This is where the arithmetic above earns its keep. A freezer build keeps its water for weeks rather than draining daily, so dosing, filtration and testing all scale off the real water volume — roughly 37 gallons in a 7 cu ft cabinet, not the 52 gallons the box claims. Dose to the wrong number and you are either wasting treatment or under-treating water you are sitting in.

Yes, and sizing it correctly is most of why. The freezer conversion wins on two things: the compressor is already in the cabinet, so you are not buying a separate chiller, and the walls are genuinely insulated, so it holds temperature well. Both advantages shrink as the cabinet grows — a bigger box means more water for the same compressor and more surface area to lose cold through. A 5 to 7 cu ft build is the version of this project that is cheaper to own than a tub-and-chiller setup. A 15 cu ft one mostly is not.

The honest comparison point is a small insulated tub with a plug-in chiller, which costs more up front, comes with a warranty, is designed for water and can be moved without two people and a dolly. If the build itself is the appeal, size it at 5 to 7 cubic feet and it is a genuinely good project. If you want cold water with no project attached, our tub roundup and 110V chiller roundup are the alternative, and neither of them voids anything.