A litter box that smells is not a box that needs more litter. It is a box on the wrong cleaning schedule. The work splits into 3 tiers: 2 scoops a day, 1 full change a week, 1 disinfect a month with a 1:32 bleach solution left in contact for 10 minutes.
Plastic boxes also expire. Scratches deep enough to catch a fingernail hold bacteria that no rinse reaches, which is why the box itself gets replaced every 6 to 12 months, not scrubbed harder.
The three tiers, and why they are not interchangeable
Daily scooping removes the load. Weekly changing removes the saturated clumps and the ammonia bound in the litter bed. Monthly disinfection kills what is stuck to the plastic. Skip the daily and the weekly change becomes a 40 minute job with a mask on; skip the monthly and the box keeps a smell the litter cannot cover, which is the most common reason a cat starts going on the floor.
A used box holds 100 to 300 ppm of ammonia at nose height within 3 to 5 days of scoop-only care, well above the 25 ppm that starts to irritate feline airways. That number, not your own nose, is the reason for the schedule: human smell adapts in about 15 minutes, a cat's nose does not.
Daily: 2 scoops, 5 minutes
Scoop at the same 2 times each day, roughly 12 hours apart, and bag the waste immediately. Cats that dig and then leave usually do it because the box already had 3 or 4 deposits in it; scooping twice a day is the single change that fixes most of that.
Top up to a depth of 5 to 8 cm. Under 4 cm and the cat reaches plastic and stops covering; over 10 cm and a small cat sinks and tracks more. Clumping clay is usually fully clumped in 15 minutes, so the second scoop of the day catches what the first one missed.
Wipe the rim and walls with a pet-safe wipe at the same time: urine sprayed over the edge dries there and is much of the smell people blame on the litter.
Weekly: the full change in 15 minutes
Empty the entire box into a bag, scrape the bottom with a plastic spatula, then wash with hot water and 1 squirt of unscented dish soap. Water at 50 to 60 degrees Celsius dissolves the urine scale that cold water leaves behind.
Rinse twice, dry with paper towel, and let the box stand in the sun for 20 to 30 minutes if you can. UV light does part of the disinfecting for free. Refill with fresh litter only after the box is completely dry, because damp litter grows bacteria on day 2.
While it is empty, look at the bottom with a light at a low angle. A network of fine lines that catches the light is the first sign the surface is going.
Monthly: 1:32 bleach, 10 minutes of contact
Mix 60 ml of household bleach into 2 litres of cool water for a 1:32 dilution, roughly 1,500 to 1,600 ppm of available chlorine. Hot water breaks bleach down and releases fumes; use cool or room temperature water and mix it fresh, since a bottle opened 6 months ago has lost much of its strength.
Pour the solution in, close the lid, and leave it for 10 minutes. Contact time is the active ingredient; a 30 second splash does almost nothing. Then pour it out, rinse 3 times with clean water, and air dry completely, lid off, for 4 to 6 hours.
Never mix bleach with a urine or ammonia based cleaner, and never with vinegar: the first combination releases chloramine gas, the second releases chlorine. If you use an enzymatic cleaner, run it as a separate step, then rinse before the bleach.
Table: dilution, contact time, and what each step removes
| Task | Frequency | Mix or setting | Contact time | Removes |
|---|---|---|---|---|
| Scoop solids | 2 per day | Slotted scoop | 2-3 min | Fresh urine and feces |
| Wipe rim and walls | 2 per day | Pet-safe wipe | 10 s | Sprayed urine film |
| Full change and soap wash | 1 per week | 50-60 C water, 1 squirt soap | 5 min | Urine scale, dust |
| Bleach soak | 1 per month | 60 ml in 2 L water (1:32) | 10 min | Bacteria, biofilm, virus |
| Sun dry | 1 per week | Direct sun | 20-30 min | Surface moisture |
| Replace plastic box | 6-12 months | New box, same size | 15 min swap | Scratched reservoir |
When the plastic box has to go
Run a fingernail along the bottom. If it catches in a groove deeper than 1 mm, the box is done: that groove holds a biofilm that bleach reaches only partly, and the smell returns within 2 or 3 days of a full change. Most plastic boxes hit that point at 6 to 12 months of daily scooping, sooner if the cat digs hard or you scoop with a metal tool.
A stainless steel pan costs 2 to 3 times a plastic one and typically lasts 5 to 10 years without scratches. A hooded box needs its carbon filter changed every 2 to 4 weeks, or it becomes a sealed jar of ammonia.
Box count and placement: cats plus one
The rule is 1 box per cat plus 1: 2 cats need 3 boxes, 3 cats need 4. In a 2 cat house with 1 box, one cat guards the entrance and the other holds urine for 12 to 20 hours, which is the road to a bladder infection and, in males, to a blockage.
Each box should be about 1.5 times the length of the cat, nose to tail base, so a 45 cm cat needs a 65 to 70 cm box. Place boxes at least 60 cm apart in different rooms, not side by side, since 2 boxes in one corner count as 1 territory. Keep every box at least 2 m from food and water, and 1 m from a wall on at least 2 sides so the cat can see out.
What the box tells you about health
Cleaning is also a daily read on the cat. Normal urine clumps are 4 to 6 cm across and a cat produces 2 to 4 of them a day; more than 5 large clumps in 24 hours, or none at all for 24 hours, is a reason to call the clinic. A male cat that squats 6 times in an hour and produces a teaspoon is an emergency, not a litter problem.
Sudden avoidance of a clean box follows a short list: a 3 day-old scoop schedule, a hood, scented litter, a box that is 2 cm too small, or pain on urination. The avoidance checklist walks through it in order, and the box itself should be built to the setup standard before you blame the cat. Write the change date on the box lid; the vaccine calendar tool makes a fine reminder for the 6 and 12 month replacement too.
Start tonight: 1 scoop before bed, 1 in the morning, litter to 5 cm, a full change on the same weekday each week, and 10 minutes of bleach on the first of the month.
Frequently asked
How often should I fully change the litter if I scoop twice a day?
Once a week for a single cat, and every 4 to 5 days in a multi-cat house. Scooping removes solids but not the ammonia bound in the litter bed, which reaches 100 to 300 ppm at nose height within 3 to 5 days. A box that still smells 10 minutes after a full change needs the monthly bleach step, not a shorter change interval.
Is bleach safe for a litter box my cat licks?
Yes, if the dilution and the rinse are right. Use 60 ml of plain household bleach in 2 litres of cool water, keep it in contact for 10 minutes, then rinse 3 times and air dry for 4 to 6 hours with the lid off. Never mix it with an ammonia or vinegar based cleaner, and never pour it into a box the cat is using, since paws pick up residue.
Do I really need to replace a plastic box that looks fine?
If a fingernail catches in a groove deeper than 1 mm, yes. Those grooves hold a biofilm that a 10 minute bleach soak only partly reaches, and the smell returns within 2 to 3 days of a fresh change. Plastic boxes reach that point at 6 to 12 months of daily scooping, while a stainless steel pan usually lasts 5 to 10 years.