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By Jason Feng, Founder & Researcher. See how this review was researched.
Quick answer
Weight ratings tell you what the scale can measure. They do not tell you whether your cat can turn around inside the globe. For a large cat, our pick is the Litter-Robot 5 at $799, which Whisker rates to 30 lbs and publishes with a 15.75-inch entryway and 17.5 inches of interior height. If your cat is tall rather than heavy, the Litter-Robot 4 at $699 has the same entryway width and 16.5 inches of interior height for $100 less.
Everything below is about matching a published opening to an actual cat.
Table of contents
- Why the weight rating is the wrong number to shop by
- Published entry and interior dimensions compared
- The ratings, the bins, and the prices
- The turn-around problem inside a moving globe
- Floor space and clearance nobody puts in the brochure
- Litter behavior changes with a bigger cat
- When a large cat shares the box with a smaller one
- How to measure your cat before you order
- Our verdict
- How we researched this
- Sources
Why the weight rating is the wrong number to shop by
A manufacturer’s cat weight range is a sensor specification. It tells you the scale is calibrated to read a cat between two numbers and to ignore weights outside that band for safety.
That is useful, and it is not the same as fit.
A 17-pound Norwegian Forest cat is long and tall. A 17-pound British Shorthair is compact. Both sit inside the same published range, and only one of them is likely to find a given globe roomy. The number on the box cannot separate them, because the box is describing a load cell, not a body.
So the specs that actually decide the purchase are the entryway dimensions, the interior height, and the interior floor area. Two of those three are published by several brands. The third almost never is.
Whisker publishes entryway and interior height for all three of its current models. PETKIT publishes dimensions and an entrance height. Petlibro publishes a single entrance figure. That is enough to build a real comparison, and it is why the table below starts there instead of with the weight range.
Published entry and interior dimensions compared
| Model | Entryway width | Interior height | Globe or cylinder volume | Cat weight range |
|---|---|---|---|---|
| Litter-Robot 5 | 15.75 in | 17.5 in | [DATA NOT VERIFIED: interior volume not published by Whisker] | 3–30 lbs |
| Litter-Robot 4 | 15.75 in | 16.5 in | [DATA NOT VERIFIED: not published] | 3–25 lbs |
| Litter-Robot EVO | 14.85 in | 14.5 in | [DATA NOT VERIFIED: not published] | 3–19 lbs |
| PETKIT Purobot Max 3 | 10.51 x 10.74 in | 8.03 in entrance | 76 L cylinder | 3.3–22 lbs |
| PETKIT Purobot Ultra | [DATA NOT VERIFIED: the entry-size block on the product page lists several SKUs together and does not label which row is the Ultra] | 10.43 in entrance | [DATA NOT VERIFIED: not published] | 3.3–22 lbs |
| Petlibro Luma | 17.4 in | [DATA NOT VERIFIED: interior height not published] | [DATA NOT VERIFIED: not published] | 2.2–22 lbs |
Read that table twice, because the columns measure different things. Whisker’s entryway figure is the width of the opening into the globe, and its interior height is the clearance above the litter bed. PETKIT’s and Petlibro’s single numbers describe the entrance, which is the hole a cat walks through.
A 15.75-inch opening and a 17.4-inch opening sound nearly the same until you remember that the Litter-Robot opening is a circular door into a globe, while the Luma entrance is a front-facing opening with a different geometry behind it. Width alone does not settle fit.
Two of these figures also move with the litter line. Whisker’s own support documentation says to fill the globe with clumping litter until it sits just below the raised fill line when spread flat, which is roughly 8 to 10 pounds, or about 1 gallon by volume. Overfill it and the usable interior height drops while the unit starts stalling mid-cycle.
For the exact numbers a Litter-Robot 4 needs in a room, including the clearance behind and beside it, our Litter-Robot 4 dimensions and fit guide walks through the measurements.
The ratings, the bins, and the prices
Weight ranges and prices come from the US product pages, fetched on 2026-10-01. Prices move with sales, so treat these as the list prices observed that day.
| Model | List price | Manufacturer cat rating | Waste capacity | Reviews on the manufacturer page |
|---|---|---|---|---|
| Litter-Robot 5 | $799 | Up to 5 cats, 3–30 lbs | Not published | 4.6/5, 241 reviews |
| Litter-Robot 4 | $699 | Up to 4 cats, 3–25 lbs | Not published | 4.5/5, 14,095 reviews |
| Litter-Robot EVO | $599 | Up to 2 cats, 3–19 lbs | Not published | 4.7/5, 35 reviews |
| PETKIT Purobot Max 3 | $399.99, listed down from $499.99 | 3.3–22 lbs | 7 L side bin | Not published on the spec block |
| PETKIT Purobot Ultra | $799.99, listed down from $899.99 | 3.3–22 lbs | 10 L bin | Not published on the spec block |
| Petlibro Luma | $599.99 | Up to 10 cats, 2.2–22 lbs | 2.9 gal, about 7 days for 2 cats | Not published on the spec block |
The Litter-Robot 5 is the only model here rated to 30 lbs, and it is the only one that pairs that rating with a 17.5-inch interior height. That combination is the reason it wins for genuinely large cats rather than merely heavy ones.
Notice what the middle of that table does. PETKIT’s two units and the Luma all top out at 22 lbs, and the EVO stops at 19 lbs. If your cat is a 20-pound Maine Coon, the EVO is out on the published range, and PETKIT and Petlibro are out at 23 lbs. You do not need a ruler for that decision, only a scale.
Whisker’s own capacity guidance is worth holding next to the cat rating. Its published figure caps the recommendation at 4 cats per unit in a household, even on the model it sells as good for 5. I would read a cat rating as a hardware ceiling, not a household plan.
The turn-around problem inside a moving globe
A self-cleaning box is not a tray. It is a rotating drum with a fixed litter bed, and your cat stands on litter that is about to tilt.
Whisker’s cycle delay setting runs from 3 to 30 minutes, with a default of 7 minutes between the cat leaving and the globe starting to move. That delay is what keeps the cycle away from a cat that is still inside, and it is also the reason a large, slow-moving cat benefits from a longer setting. Five green lights on the light bar mean the delay is set to 30 minutes.
Inside the globe, the usable footprint is set by the litter bed, not by the outer shell. A long cat needs room to step in, turn, and squat without its rear touching the back of the globe. That is where interior height and entry width combine, and it is why a wide opening on a shallow globe can still be cramped.
PETKIT describes the Max 3 with a 76 L cylinder and a deliberately low entry threshold, and its entry measures 10.51 by 10.74 inches with an 8.03-inch entrance height. That is a genuinely low step for a big cat to clear. It is also a smaller opening than Whisker’s, so a very large cat will meet a tighter door before it meets a tighter drum.
This is the part of the comparison the spec sheets do not finish for you. I would treat entry width as the gate and interior height as the ceiling, and treat whatever is left as the part you learn by watching your cat use it.
Floor space and clearance nobody puts in the brochure
| Model | Footprint (W x D) | Overall height | Empty weight |
|---|---|---|---|
| Litter-Robot 5 | 22 x 27 in | 29.9 in | 28.7 lbs |
| Litter-Robot 4 | 22 x 27 in | [DATA NOT VERIFIED: not listed in the spec block we fetched] | 24 lbs |
| Litter-Robot EVO | 20.6 x 24.3 in | 27.6 in | 21.5 lbs |
| PETKIT Purobot Max 3 | 24.4 x 21.2 in | 21.7 in | 22 lbs |
| PETKIT Purobot Ultra | 20.94 x 32.20 in | 24.09 in | about 32.18 lbs |
| Petlibro Luma | 23.3 x 22.5 in | 28.1 in | 33.01 lbs |
Two things fall out of that table.
First, a self-cleaning box is furniture. The Litter-Robot 5 stands nearly 30 inches tall and covers roughly 4 square feet of floor, and the Ultra runs more than 32 inches deep. In a small apartment, the footprint is the constraint long before the cat rating is.
Second, clearance matters as much as footprint. Petlibro’s Luma guide asks for about 4 inches of space around the unit so the weight sensor reads correctly. Whisker’s fault documentation is stricter about surfaces than about gaps: a unit on carpet, a litter mat, a power cord, a grout line, or touching a wall can hold the scale in a false occupied state and stop cycling. For a large cat, that placement discipline matters, because a bigger cat puts more weight on a scale that is already being confused by the floor.
If the box has to live inside a piece of furniture, read the caveats first. Our guide to litter box enclosures covers what a cabinet does to airflow and to the largest cats in the house.
Litter behavior changes with a bigger cat
A large cat moves more litter per visit.
Volume per trip goes up, so the clumps are bigger and heavier, and the sifting mechanism encounters more mass. Whisker’s support documentation names overfilled litter as a direct cause of cycling issues, and the overtorque fault is documented as litter or weight exceeding what the globe can turn against. A big cat plus a full globe is the fastest route to that fault.
Litter type matters for the same reason. Fine clumping litters sift cleanly; light or dusty litters track more and coat the sensors. If you are choosing litter for a machine and a large cat at once, our breakdown of litter types for automatic boxes covers which formats hold up under heavy rotation.
Depth is one setting a large cat owner can actually tune. Whisker’s stated fill is a range, not a fixed line, and staying at the low end of it keeps the globe from working against extra weight. The trade-off is a shallower bed, which some cats dislike. Start near the published line and adjust down if the unit reports weight faults.
When a large cat shares the box with a smaller one
Size differences inside one household create a problem the weight range hides.
A 20-pound cat and an 8-pound cat both fall inside the published range of most units here. What differs is how each one fits the opening and how each one triggers the sensor. Whisker sets a floor of 3 lbs before automatic mode is safe, and both PETKIT and Petlibro warn about kittens, with Petlibro instructing owners of kittens under 6 months to switch auto-cleaning off entirely.
The larger risk is social rather than mechanical. A big cat that claims the box can make a smaller cat wait, and a self-cleaning unit is unavailable while it cycles. Whisker’s own guidance points owners toward a second, plain box in a different room for exactly this reason.
For the household math, our automatic litter box guide for multiple cats works through capacity and the n+1 rule. The short version: one machine does not replace a second location.
How to measure your cat before you order
Four measurements, taken with a soft tape, will settle most of this.
Measure your cat’s length from nose to base of tail while it stands. Measure its standing height at the shoulder and at the top of the head. Measure the width across the ribs. Weigh it on a baby scale or at the vet, since a bathroom scale plus subtraction introduces too much error.
Then compare. A cat whose nose-to-tail length approaches the entry width will fold itself through that opening every day, and some cats accept that while others do not. A cat that stands taller than the published interior height cannot use the globe in the posture the manufacturer intended, which usually shows up as the cat hanging its rear outside the door.
The other measurement is your room. Mark the footprint on the floor with tape, add the clearance the manufacturer asks for, and walk the route your cat would take to reach it. A large cat that has to turn sideways to reach the entry is a cat that may choose your laundry basket instead.
If you already own a Litter-Robot 4, the dimension walkthrough converts those figures into a checkable list. For the wider field, our automatic litter box roundup compares the category model by model.
Our verdict
Buy the Litter-Robot 5 at $799 if your cat is large in any direction. It is the only current model here rated to 30 lbs with a 17.5-inch interior height and a 15.75-inch entryway, and it takes any waste bag that fits the drawer.
Buy the Litter-Robot 4 at $699 if your cat is long but under 25 lbs. You keep the 15.75-inch entryway and give up an inch of interior height for $100, and you gain the deepest published review base in the category at 14,095 manufacturer-hosted reviews.
Buy the PETKIT Purobot Max 3 at $399.99 if your cat is under 22 lbs and the priority is a low entry step and a big waste bin. It publishes a 76 L cylinder and a 7 L side bin, and it costs less than any Whisker model.
Buy the Petlibro Luma at $599.99 if your cat is tall and under 22 lbs. Its 17.4-inch entrance is the widest single opening in this table, though the interior height behind it is not published and the unit is the heaviest here at 33 lbs.
Do not buy the Litter-Robot EVO at $599 for a cat over 19 lbs, whatever the price. The published weight ceiling disqualifies it for the cats this article is about.
One last caution. Every number above is a manufacturer claim about its own product, and prices move. Weigh your cat, measure the space, then verify the current spec block before you order.
How we researched this
- Every dimension, weight range, price, and volume figure here was read from the manufacturer’s own US product page on 2026-10-01, fetched through a US proxy with an en-US language header so US pricing and US model variants were returned.
- Where a spec block did not label a row, or did not publish a figure at all, we marked it
[DATA NOT VERIFIED]rather than inferring it from a sibling model. The PETKIT entry-size block and the interior volumes are flagged for that reason. - Placement and litter-fill behavior comes from Whisker’s published support articles, including the litter quantity guide, the cycle delay settings page, and the fault articles for overtorque and excess weight.
- This is a research-based review. Specifications come from manufacturer documentation, with owner-reported failure patterns aggregated across public reviews and community threads.
- Review counts and ratings are as displayed by the manufacturer on the fetch date and are not independent measurements.
Read more about how we research and our affiliate disclosure.
Sources
Fetched on 2026-10-01 through a US egress with an en-US language header:
- https://www.litter-robot.com/litter-robot-5.html
- https://www.litter-robot.com/litter-robot-4.html
- https://www.litter-robot.com/litter-robot-evo.html
- https://www.whisker.com/litter-robot-comparison-chart
- https://www.litter-robot.com/support/article/how-much-litter-do-i-put-in-litter-robot/
- https://www.litter-robot.com/support/article/litter-robot-4-wait-time-settings
- https://www.litter-robot.com/support/article/litter-robot-4-red-with-partial-yellow-flashing-over-torque-fault/
- https://www.litter-robot.com/support/article/litter-robot-4-blue-yellow-flashing-excess-weight-detected/
- https://www.litter-robot.com/blog/how-many-litter-robots-for-how-many-cats/
- https://www.petkit.com/products/purobot-max-3-automatic-cat-litter-box
- https://www.petkit.com/products/purobot-ultra
- https://petlibro.com/products/luma-smart-litter-box
- https://petlibro.com/pages/how-to-address-the-placement-error