The core problem: ammonia from urine breaks down fast

Cat urine smells because it contains urea, which bacteria break down into ammonia within hours. You cannot stop this chemical reaction, but you can remove the urine before it happens or neutralize the ammonia after. The difference between a litter box that smells and one that does not is usually daily scooping, litter depth, and box size—not expensive additives or special litters.

Most odor comes from wet clumps sitting in the box, not from solid waste. A cat that urinates four times a day in a box you scoop once will have ammonia building up for 24 hours. The math is straightforward: more frequent removal stops the smell before it starts.

Key Takeaways

  • Scoop the litter box at least once daily, ideally twice, to remove urine clumps before ammonia forms.
  • Use clumping litter at least 2 to 3 inches deep so urine soaks into the litter instead of pooling at the bottom.
  • A box that is too small forces urine and feces close together, which speeds up odor; the rule is one box per cat plus one extra.
  • Baking soda sprinkled on top of fresh litter absorbs some ammonia, but it works only if you scoop regularly first.
  • Replace the entire litter box contents every 1 to 2 weeks, depending on how many cats use it and how often you scoop.

Scoop once or twice daily to stop ammonia before it forms

Scooping is the single most effective odor control. When you remove a wet clump within a few hours of urination, the bacteria have not yet broken down the urea into ammonia. By the time you notice a smell, the ammonia is already in the air and in the litter around the clump.

Once-daily scooping works for a single cat in a large box, but twice daily is more reliable. Morning and evening takes five minutes total and removes almost all odor before it builds up. If you have multiple cats, scoop after the busiest times of day—usually morning and evening.

Use a scoop with a handle long enough that you do not have to bend far, and shake the scoop over the box for a few seconds so fine litter falls back through. This saves litter and keeps dust down.

Use clumping litter at least 2 to 3 inches deep

Clumping litter absorbs urine and forms a solid mass you can remove whole. Non-clumping litter absorbs urine but does not clump, so you cannot remove the wet section—it stays in the box and breaks down into ammonia. If you use non-clumping litter now, switching to clumping will cut odor noticeably within a week.

Depth matters because shallow litter lets urine soak through to the bottom of the box, where it pools and sits. Two to three inches is the standard depth. If you use less, urine reaches the plastic bottom and sits there even after you scoop the clump above it. If you use more than 4 inches, you waste litter and cats may refuse to dig.

Most clumping litters are clay-based and work similarly. Brand differences are small. Unscented clumping litter is cheaper than scented and does not mask odor with perfume—it straightforward removes the source. If your cat has been using one brand for months, switching suddenly can cause them to avoid the box, so mix the new litter in gradually over a week.

Size and number of boxes: one per cat plus one extra

A litter box that is too small forces urine and feces close together, which speeds decomposition and odor. The box should be at least 1.5 times the length of your cat from nose to tail base. Most standard boxes are 22 by 16 inches, which works for most cats, but large cats need a storage container or a jumbo box instead.

Multiple cats in one box create odor faster because urine accumulates more quickly. The standard rule is one box per cat plus one extra. A household with two cats should have three boxes. This sounds excessive but works because each cat has a box they prefer, and the extra box catches overflow. Boxes should be in different rooms or at least different corners of the same room.

If you have only one box and multiple cats, odor will be worse no matter how often you scoop. Adding a second box usually cuts odor by half within days because each cat urinates less frequently in their preferred box.

Replace all litter every 1 to 2 weeks, not just spot-clean

Scooping removes clumps, but fine litter at the bottom absorbs urine over time and becomes saturated. Even if you scoop daily, the base layer is slowly filling with urine that you cannot see. After 1 to 2 weeks, this layer smells and needs to be thrown out and replaced.

For a single cat with daily scooping, every 2 weeks is usually enough. For multiple cats or if you scoop less often, do it weekly. To replace the litter, dump the entire box into a trash bag, wipe the plastic bottom with a damp cloth, and refill with fresh litter.

Some people add baking soda to the bottom of the box before pouring in fresh litter. Baking soda absorbs some ammonia, but only if the litter above it is being scooped regularly. If you are not scooping, baking soda will not help.

Baking soda and other odor absorbers: what actually works

Baking soda sprinkled on top of fresh litter absorbs some ammonia smell. Use about a tablespoon per box. It is cheap and harmless to cats. However, it only works if you are already scooping regularly—it cannot neutralize ammonia that is already in the air or deep in the litter.

Activated charcoal works similarly and is sometimes sold in litter box liners or as a separate product. It absorbs odor but again only if the box is being maintained. Enzymatic litter additives claim to break down urine compounds, but they are not necessary if you scoop daily and replace litter weekly.

Scented litters and litter box sprays mask odor rather than remove it. They can make a neglected box smell like perfume and ammonia together, which is worse. If your box smells, the problem is not the scent—it is the maintenance routine.

Box placement and ventilation matter more than you think

A litter box in a closed bathroom or corner with no air movement will smell stronger than the same box in a room with a window or fan. Ammonia is a gas, and it concentrates in still air. If your box is in a basement corner, moving it to a room with better air flow will noticeably reduce odor even if nothing else changes.

Avoid placing the box directly next to food or water bowls, which is uncomfortable for the cat and can cause them to avoid the box. A box in a laundry room, mudroom, or bathroom with a window is ideal. If you have no good location, a small fan pointed at the box helps push ammonia away.

Litter box liners and covers can trap odor. A liner makes cleanup easier but also traps ammonia inside the box. If you use a liner, choose one with ventilation holes or skip it entirely. Covered boxes look neater but concentrate odor inside—open boxes ventilate better.

When to call a vet: medical issues that cause extra odor

If you are scooping daily, using clumping litter at proper depth, and replacing litter weekly but the box still smells unusually strong, your cat may have a urinary tract infection or other medical issue. Cats with UTIs urinate more frequently and sometimes outside the box. Cats with kidney disease or diabetes also urinate more.

If the smell is new and your routine has not changed, contact your veterinarian. They can test for infection or other conditions. Do not assume the smell is a litter problem if the cat's behavior has changed.

Frequently Asked Questions

How often should I completely empty and refill the litter box?

For one cat with daily scooping, every 1 to 2 weeks is standard. For multiple cats or less frequent scooping, do it weekly. Dump the entire contents, wipe the box bottom with a damp cloth, and refill with fresh litter. The fine litter at the bottom absorbs urine over time even if you scoop clumps daily.

Does expensive litter work better than cheap clumping litter?

Most clumping litters work similarly because they are all clay-based. Brand differences are small. Unscented clumping litter is usually cheaper and works as well as premium brands. The money matters more in box size, number of boxes, and scooping frequency than in litter choice.

Can I use baking soda instead of litter additives?

Yes. Sprinkle about a tablespoon of baking soda on top of fresh litter. It absorbs some ammonia and costs much less than commercial additives. It only works if you are scooping regularly—it cannot neutralize odor that is already in the air or deep in the litter.

Why does my cat avoid the litter box even though I scoop daily?

The box may be too small, in an uncomfortable location, or the cat may have a medical issue. Cats also avoid boxes that are too close to food or water, or boxes that are covered. Try adding a second box in a different room, or switching to a larger open box. If the cat still avoids it, contact your veterinarian.

Does a covered litter box reduce smell?

Covered boxes look neater but actually trap odor inside rather than letting it ventilate. Open boxes allow ammonia to disperse into the room, where you notice it and are motivated to scoop. If odor control is your goal, an open box with regular scooping works better than a covered one.