Short answer
For a corded robot, roughly its cable length minus the depth of the deep end — a 60 ft cable reaches about a 52 ft pool. For a cordless one, as much floor and wall as its battery can cover: at 13 sq ft a minute, a full floor-and-wall pass of a 16 × 32 ft pool (about 992 sq ft) takes around 76 minutes. By that arithmetic, 11 of the 29 cordless robots here with a runtime to check claim a noticeably bigger pool than their battery covers.
The power supply sits on the deck, usually near the middle of one side. From there the cable runs down the wall to the floor before the robot can travel anywhere, so the depth of the deep end is cable the robot cannot use for distance. This site takes 8 feet as a typical residential deep end and calls the rest the usable pool length:
usable pool length = cable length − 8 ft
It is deliberately simple. A power supply placed at the middle of a long side needs less reach than one in a corner, and a shallow pool gives some of the allowance back. A maker claim more than 2 ft past that figure is flagged on the robot's page; within 2 ft, the difference is placement.
A cordless robot's reach is its runtime multiplied by how much surface it covers a minute. Nobody publishes that pace, so this site takes it from the one maker whose ratings let it be worked out: Maytronics rates its 50-foot robots for a 2.5-hour cycle, and a 50 × 25 ft pool with a 5 ft average depth has about 2,000 sq ft of floor and wall. That is about 13 sq ft a minute.
The pool is modelled as a 2:1 rectangle, L long and L/2 wide, at a 5 ft average depth. Its floor is L²/2 and its walls are 2 × (L + L/2) × 5 = 15·L. A full pass needs (L²/2 + 15·L) ÷ 13 minutes, and solving for L gives the longest pool the runtime covers.
Where the maker publishes only a floor-only runtime, the walls are left out and the verdict says “floor only”. That is the generous reading: a robot rated for four hours on the floor will not manage four hours climbing walls, which work its motors harder.
| Pool | Floor + wall area | Minutes at 13 sq ft/min |
|---|---|---|
| 20 × 10 ft | 500 sq ft | 38 |
| 32 × 16 ft | 992 sq ft | 76 |
| 40 × 20 ft | 1,400 sq ft | 108 |
| 50 × 25 ft | 2,000 sq ft | 154 |
| 60 × 30 ft | 2,700 sq ft | 208 |
Cordless makers mostly quote pool size in square feet of plan area — the footprint of the pool, as if the robot only had to cover the floor, once. Walls are real surface: a 16 × 32 ft pool has nearly as much wall as floor. And the runtime a maker quotes beside the rating is often the floor-only or eco figure, not the one for a full cycle.
To compare a square-foot claim with a pool length, this site converts it to the length of a 2:1 rectangle with the same area (length = √(2 × area)), then checks it against what the runtime covers. A claim more than 10 % beyond the arithmetic is flagged. 11 robots are flagged today; the guide listing them is linked below.
Cordless floor+wall+waterline · 270 min, floor + walls
Cleans: Floor, walls, waterline, surface
Cordless floor+wall+waterline · 150 min, floor + walls
Cleans: Floor, walls, waterline
Cordless floor+wall+waterline · 240 min, floor + walls
Cleans: Floor, walls, waterline
Corded if the pool is large or you want the robot to run on a schedule for years without a battery to replace; cordless if the cable is the thing you hate. A corded robot never runs out mid-cycle and has no battery to wear out, but its cable twists over time. A cordless one has no cable to tangle, but its runtime is the hard limit on what it can clean, and its battery loses capacity every season.
A robot is the only one of the three that works independently of your pool's pump and filter: it has its own motor, its own filter and its own power supply, so it catches debris on board instead of sending it to the skimmer basket and filter. Suction-side cleaners are the cheapest to buy and use the pump's suction; pressure-side cleaners use the pump's return flow, often with a booster pump, and carry a bag. If the pool filter is small or the pump is old, a robot takes load off both.
Every specification explained, with the numbers from the catalog behind each one.