Of the two, the Litter-Robot 4 is the one you can still buy: Whisker has discontinued the Litter-Robot 3 Connect in the U.S., and its reconditioned stock on Oct 17, 2026 held no Litter-Robot 3. The 4 stands on a base 2.25 in (5.7 cm) narrower at the same 29.5 in (75 cm) height, with an opening 5.5 in (14 cm) wider.
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Which Litter-Robot to choose for a small apartment
For one to four cats of 3 to 25 lb, get the Whisker Litter-Robot 4: the 3 is discontinued in the U.S., and the 4 gives a cat a wider door and more headroom than the smaller EVO.
Measure your cat before you order. An average adult is 18 to 20 in (46 to 51 cm) long, nose to tail base, so the AAFP and ISFM guideline of 1.5 times that length means a box of 27 to 30 in (69 to 76 cm), longer than the 4’s 19 x 18 in (48 x 46 cm) globe; the cat measuring tool gives your cat’s number.
Will it fit? Whisker Litter-Robot 4
- Footprint
- 22 x 27 in (56 x 69 cm), 4.1 sq ft (0.38 m²)
- Height
- 29.5 in (75 cm)
- Needs around it
- About 1 in (2.5 cm) from the wall, by Whisker’s FAQ
- Best for
- One to four cats weighing 3 to 25 lb (1.4 to 11.3 kg)
- Skip if
- Your only free spot is a damp bathroom
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.Match the model to your cat first:
- Choosing between the 3 and the 4The Litter-Robot 4.$699.00 Price as of Nov 3, 2026, 04:24 UTCCheck price at Amazon
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product. - One cat under 19 lb in a tight corner, or a cat that needs the lowest stepThe EVO, at 5.6 in (14 cm).$599.00 Price as of Nov 3, 2026, 04:24 UTCCheck price at Amazon
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product. - Over 25 lb, or a tall breedThe Litter-Robot 5, or the Pro for cameras.
- Room for 22 in (56 cm) of height but not 28The PETKIT, for a nimble cat on clumping litter.$399.99 Price as of Nov 3, 2026, 04:24 UTCCheck price at Amazon
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product. - No headroom at all, and a cat already on crystalsThe ScoopFree.$129.99 Price as of Nov 3, 2026, 04:24 UTCCheck price at Amazon
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
Key takeaways
- The 4’s door is a 15.75 in (40 cm) square, the 3 Connect’s 10.25 in (26 cm) wide. → what changed
- Bathrooms are probably out: Whisker’s FAQ says moisture can damage the components. → placement
- Only the discontinued 3 Connect’s page says it cannot join shared apartment Wi-Fi; the 4 needs a 2.4 GHz network. → Wi-Fi
- A cat straining with little or no urine needs a vet right away. → vet note
Litter-Robot 3 vs 4, the EVO and the 5: specs side by side
The table adds Whisker’s newer EVO and Litter-Robot 5, plus two lower boxes from other makers. Weights are for the empty unit.
| Model | Footprint (W x D) | Height | Opening width | Inside height | Step height | Empty weight | Cats, by the maker |
|---|---|---|---|---|---|---|---|
| Whisker Litter-Robot 4 | 22 x 27 in (56 x 69 cm) | 29.5 in (75 cm) | 15.75 in (40 cm) | 16.5 in (42 cm) | 6.9 in (18 cm) | 24 lb | 3 to 25 lb, up to 4 cats |
| Whisker Litter-Robot 3 Connect, discontinued | 24.25 x 27 in (62 x 69 cm) | 29.5 in (75 cm) | 10.25 in (26 cm) | 15 to 17 in (38 to 43 cm) | 7.1 in (18 cm) | 24 lb | From 5 lb, no upper limit |
| Whisker Litter-Robot EVO | 20.6 x 24.3 in (52 x 62 cm) | 27.6 in (70 cm) | 14.85 in (38 cm) | 14.5 in (37 cm) | 5.6 in (14 cm) | 21.5 lb | 3 to 19 lb, up to 2 cats |
| Whisker Litter-Robot 5 and 5 Pro | 22 x 27 in (56 x 69 cm) | 29.9 in (76 cm) | 15.75 in (40 cm) | 17.5 in (44 cm) | 7 in (18 cm) | 28.7 lb; Pro 29.6 lb | 3 to 30 lb, up to 5 cats |
| PETKIT Purobot Max 3 | 24.4 x 21.2 in (62 x 54 cm) | 21.7 in (55 cm) | 10.51 in (27 cm) | Not given | 8.03 in (20 cm) entry | 22 lb | 3.3 to 22 lb, from 6 months |
| PetSafe ScoopFree Crystal Pro Legacy, uncovered | 27.6 x 19.1 in (70 x 49 cm) | 6.2 in (16 cm) | Open top | Open top | Not given | 13.3 lb (listing) | Listing: from 6 months |
A 3’s inside height varies with the litter level. From above, these boxes differ far less in floor than in height:
What changed from the Litter-Robot 3 to the Litter-Robot 4
Most of the change is at the door: a 3 Connect opens 10.25 in (26 cm) wide, a 4 offers a 15.75 in (40 cm) square over a step of 6.9 in (18 cm) instead of 7.1. Whisker also cut the base from 24.25 to 22 in (62 to 56 cm) wide at the same 27 in (69 cm) depth, freeing about 0.4 sq ft (0.04 m²).
Inside, the floor went the other way: Whisker’s FAQs give the 3’s globe 20 x 20 in (51 x 51 cm) and the 4’s 19 x 18 in (48 x 46 cm). By the same guideline, even a short 16 in (41 cm) cat needs a 24 in (61 cm) box, and both globes fall short.
A 3 cycles on its own only for a cat of 5 lb (2.3 kg) or more. Its successor adds laser sensors and starts at 3 lb (1.4 kg). Whisker’s chart caps the 4 at 25 lb (11.3 kg), though one support FAQ says it has no weight limit, and the 3’s page gives it none.
Whisker calls the 4’s drawer enlarged, good for about 8 days with one cat, but gives no figure for the 3’s. The 4 also tracks litter and drawer levels in the app, while only the 3 Connect works with IFTTT and other smart home products.
Litter-Robot 4: our pick for a small apartment
Choose the Whisker Litter-Robot 4 if the choice is between these two. It suits a small home best on Whisker’s specs and its record: listed on Amazon since July 2022, sold new and reconditioned with a 1-year WhiskerCare warranty and an optional 3-year plan, on a narrower base than the 3. Its scale wants a firm floor, or Whisker’s Carpet Tray on carpet 3 mm or thicker.
Litter-Robot 3 Connect: discontinued in the U.S.
Whisker’s 3 Connect page now says it is no longer available and points buyers to the EVO or the 5, and its FAQ adds that parts, warranty service and support continue for owners. Buying used, check three things: WhiskerCare runs 1 year from Whisker’s ship date, with no extended plans sold for the 3; the sensor needs a 5 lb cat; and the 3 Connect’s Wi-Fi rules below are stricter than the 4’s.
Weight minimums and fakes. A kitten under 3 lb (1.4 kg), or 5 lb for a 3, is too light for the sensor: Whisker says to leave the unit off and, about 7 minutes after each visit, switch it on for one clean cycle, then back off. It also warns that counterfeit Litter-Robots often lack its safety technology and will not service them, so buy from Whisker’s sites, its Amazon store or a named retailer.
Litter-Robot EVO: the smallest globe Whisker makes
The Whisker Litter-Robot EVO sits 1.9 in (4.8 cm) lower, weighs 2.5 lb less and needs 0.65 sq ft (0.06 m²) less floor than the 4. Whisker aims it at one-cat homes and smaller spaces, for up to two cats of 3 to 19 lb. The savings come out of the globe, with a 14.85 in (38 cm) opening and 14.5 in (37 cm) of headroom; Whisker steers large or tall cats to the 4 or 5. It flags only a full drawer, about weekly for one cat, and Amazon first listed it on Dec 11, 2025.
Will it fit? Whisker Litter-Robot EVO
- Footprint
- 20.6 x 24.3 in (52 x 62 cm), 3.5 sq ft (0.33 m²)
- Height
- 27.6 in (70 cm)
- Step
- 5.6 in (14 cm), the lowest of the Litter-Robots
- Best for
- One cat under 19 lb (8.6 kg) in the tightest corner, carpet included
- Skip if
- Your cat is tall, long or near that cap
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.Litter-Robot 5 vs 4, and the 5 Pro: the same floor, more headroom
The Litter-Robot 5 keeps the 4’s footprint and adds an inch of inside height. Whisker rates it for up to five cats of 3 to 30 lb (13.6 kg), with a drawer that lasts about 10 days for one cat, a built-in carpet tray and WasteID, which tells urine from stool to time each cycle. It weighs 28.7 lb (13 kg) empty, and the Pro adds two 1080p cameras and 5 GHz Wi-Fi. Whisker calls it its latest generation and sells it on its own sites, litter-robot.com and whisker.com. We link the 4 because Amazon carried no Whisker listing for the 5 or the Pro on Oct 17 or Oct 27, 2026. At 4.7 lb (2.1 kg) heavier on the same floor, the 5 earns its place for a cat above 25 lb or a tall breed.
If no globe fits: two lower automatic boxes
Every Litter-Robot stands at least 27.6 in (70 cm) tall. Two other makers build lower.
The PETKIT Purobot Max 3 is a rotating-drum box 21.7 in (55 cm) tall, 7.8 in (20 cm) lower than a 4. PETKIT lists cats of 3.3 to 22 lb from 6 months, a bin lasting up to 15 days for one cat, sensors that stop the drum if a cat steps in, and 2.4 GHz Wi-Fi. Its 8.03 in (20 cm) entry is higher than any Litter-Robot step; skip it for a stiff cat.
The PetSafe ScoopFree Crystal Pro Legacy has no drum: sensors start a clean once the cat has left, and a throwaway tray of crystal litter lasts up to 30 days, PetSafe says. Uncovered, it stands 6.2 in (16 cm) high. It takes only PetSafe’s crystal litter, and the AAFP and ISFM and Cornell say most cats prefer fine, unscented clumping litter, so choose it only for a cat already on crystals.
Will a Litter-Robot 4 fit your bathroom or closet?
Probably not the bathroom. Whisker’s FAQ suggests keeping a Litter-Robot out of it, because moisture can damage its components, and asks for a firm floor about an inch from the wall. In a studio that rules out the usual spot; our small-apartment placement guide weighs the closet, the hallway and the end of a sofa instead. Before ordering, measure:
- Floor: 22 x 28 in (56 x 71 cm) for the 4 with its wall gap, 20.6 x 25.3 in (52 x 64 cm) for the EVO.
- Height: 29.5 in (75 cm), or 29.9 in (76 cm) for a 5.
- Headroom: cleaning every 1 to 3 months means lifting off the bonnet, then the globe, by hand, so keep the space above clear.
The space-fit planner checks a 22 x 28 in (56 x 71 cm) rectangle against the spot you measured.
Noise through a shared wall at night
We found no decibel rating for any Litter-Robot on Whisker’s pages. Whisker says QuietSift cycles won’t wake you at night, which tells you nothing about what a neighbor hears through a shared wall; PETKIT, by contrast, claims 45 dB for its Purobot Max 3.
Timing is what you control. A 3-second press of the 4’s Cycle button starts sleep mode: no automatic cycles for 8 hours, repeating every 24, adjustable in the app, with one clean cycle at the end if a cat visited. Set it at bedtime. The wait after each visit can run from 3 to 30 minutes.
Wi-Fi and the Whisker app in a rental
Wi-Fi is optional: Whisker says a Litter-Robot cleans itself without it. To connect, every Litter-Robot needs a 2.4 GHz network except the 5 Pro, which also takes 5 GHz. Whisker’s help pages want the network visible and password-protected, with a password of 8 to 31 characters free of slashes, periods, @ signs, apostrophes and spaces. Only the 3 Connect page goes further: it takes IPv4 addressing only and says those robots cannot join shared networks in apartment complexes or college dorms. Whisker’s pages for the 4, EVO and 5 say nothing about shared networks, so it states no such limit for them. A building network that sends you to a login page is still a risk, so a router or hotspot of your own is the safe test.
The outlet, the cord and a power cut
Each Litter-Robot runs from a 15 V DC adapter in a wall outlet, and no Whisker page we read gives a cord length, so measure first. Whisker’s backup battery for the 4, 5 and EVO, model UB1213k, keeps cycles going for 24 to 48 hours in an outage and recharges afterward. The 3 needs its own kit, and the battery does not support the LitterHopper. Without one, scoop by hand until the power returns.
Stairs, returns and the carton
Carry the unit up a walk-up before adding litter: 21.5 lb for an EVO, 24 lb for a 4. Whisker recommends a standard-weight clumping clay, so the litter stays heavy too; our guide to litter types compares the main kinds. Whisker’s own sales carry a 90-day in-home trial, though you pay return shipping and must clean the unit; Amazon orders go back under Amazon’s terms. Keep the carton until your cat uses the box.
Who should skip an automatic litter box
Whisker says most cats take to a Litter-Robot within a week. We would wait with:
- A kitten under the sensor minimum, unless you will run each cycle by hand.
- A fearful cat: San Diego Humane advises letting it explore the new box unplugged, with the old one still out, and behaviorist Mikel Delgado, writing for AVSAB, says to avoid these boxes.
- More cats than the maker’s limit of two, four or five.
- Any cat on pine pellets or another non-clumping litter, which Whisker lists as incompatible.
Whisker also says one Litter-Robot 4 removes the need for several boxes. The AAHA and AAFP guidelines still call for one box per cat and one extra, and we found no veterinary guideline or study that takes a position on self-cleaning boxes. Count the robot as one; our two-cat litter box guide places the rest.
Keep checking what the box collects. The AAFP and ISFM favor open boxes partly so owners can see what is in them, and an automatic box takes that daily look away. Glance at the drawer, read the visit log if you use the app, and watch your cat in the box now and then. A cat that strains and passes little or no urine, most often a male, needs a vet right away: Cornell warns that a complete blockage can be fatal within 24 to 48 hours, and iCatCare notes that owners can mistake the straining for constipation.
How these models were chosen
The question was the 3 against the 4, so those two set the frame, and Whisker’s EVO and Litter-Robot 5, a PETKIT and a PetSafe ScoopFree joined for homes with less height. All were compared on footprint, height, door width, inside headroom and the cat weights each maker lists. The 3 no longer ships in the U.S. and Whisker’s reconditioned stock held none, which settled the pick. Whisker’s pages carry no decibel rating, so noise is not ranked.
Questions about the Litter-Robot 3, 4 and 5
Is the Litter-Robot 3 still sold?
Not by Whisker in the U.S., new or refurbished: the 3 Connect page calls it no longer available, and the reconditioned list on Oct 17, 2026 held only the 4, EVO and 5. Used units still change hands, and Whisker still sells parts and supports owners.
Litter-Robot 4, 5 or EVO for a studio apartment?
For one cat under 19 lb, the EVO saves about 0.65 sq ft (0.06 m²) and 1.9 in (4.8 cm) of height. A 4 suits a heavier cat or up to four cats, and it reports the litter level. The 5 needs the 4’s floor and weighs 4.7 lb (2.1 kg) more, which pays off for cats over 25 lb.
Can a Litter-Robot go in a small bathroom?
Whisker advises against it, because bathroom moisture can harm the electronics, and it offers no workaround. Better to give the bathroom an ordinary box and put the robot in a dry spot, such as a closet or a hallway corner, on a firm floor with about 1 in (2.5 cm) of gap to the wall.
Will a Litter-Robot connect to my apartment building’s Wi-Fi?
It can be a problem. It needs a visible, password-protected 2.4 GHz network. Only the discontinued 3 Connect’s page says its robots cannot use shared apartment-complex networks; the pages for the 4, EVO and 5 do not mention them. Test with a router or hotspot of your own first, or go without the app: the box still cleans itself, minus the logs and alerts.
Next step. Try the globe’s footprint on your actual corner in the space-fit planner before you choose between them.
Sources
- Whisker, “Litter-Robot 3 Connect,” litter-robot.com, read Oct 17, 2026.
- Whisker, “Litter-Robot 4,” litter-robot.com, read Oct 17, 2026.
- AAFP and ISFM, “Guidelines for Diagnosing and Solving House-Soiling Behavior in Cats,” Journal of Feline Medicine and Surgery, 2014, journals.sagepub.com, read Oct 16, 2026.
- Whisker, “Litter-Robot 4: Frequently Asked Questions,” litter-robot.com, read Oct 17, 2026.
- Whisker, “Litter-Robot FAQ,” litter-robot.com, read Oct 17, 2026.
- San Diego Humane Society, “Litter Boxes 101,” sdhumane.org, read Oct 16, 2026.
- Whisker, “Compare Litter-Robot models,” whisker.com, read Oct 17, 2026.
- Whisker, “Litter-Robot EVO,” whisker.com, read Oct 17, 2026.
- Cornell Feline Health Center, “Feline behavior problems: house soiling,” vet.cornell.edu, read Oct 16, 2026.
- Whisker, “Litter-Robot 5,” litter-robot.com, read Oct 17, 2026.
- PETKIT, “Purobot Max 3 Automatic Cat Litter Box,” petkit.com, read Oct 17, 2026.
- Whisker, “Reconditioned robots,” whisker.com, read Oct 17, 2026.
- Whisker, “Litter-Robot 4: Purple light bar (Sleep mode),” litter-robot.com, read Oct 17, 2026.
- PetSafe, “ScoopFree Crystal Pro Legacy Self-Cleaning Litter Box,” petsafe.com, read Oct 17, 2026.
- Whisker, “Litter-Robot 4 Backup Battery,” litter-robot.com, read Oct 17, 2026.
- AAHA and AAFP, “2021 Feline Life Stage Guidelines: general litter box considerations,” aaha.org, read Oct 16, 2026.
- Whisker, “Whisker App Onboarding: Unable to select WiFi network,” litter-robot.com, read Oct 17, 2026.
- Whisker, “Counterfeit Litter-Robot products,” litter-robot.com, read Oct 17, 2026.
- Cornell Feline Health Center, “Feline lower urinary tract disease,” vet.cornell.edu, read Oct 16, 2026.
- International Cat Care, consensus guidelines on lower urinary tract diseases, 2025, PubMed Central, read Oct 16, 2026.
- American Veterinary Society of Animal Behavior, “What does the science say about cats and covered litter boxes?,” avsab.org, read Oct 16, 2026.
