One cat gets through 10–15 kg of clumping litter a month: about 1.5–3 kg a week in top-ups plus a 4–5 kg full change. At $1.00–1.55 per kilo that is $12–22 a month, or $150–260 a year. Tofu litter costs 3–4 times more per kilo and lands at $30–55 a month. Pine pellets look cheapest on the shelf and are not, because you dump the whole box every week.
The 10–15 kg baseline
The number is built from two habits. Scooping twice a day and topping up keeps the box at a 7–10 cm depth, which takes 1.5–3 kg a week for one cat. A full change every 2–4 weeks takes another 4–5 kg. Do the arithmetic once and the monthly bag count stops being a surprise: 4 × 1.5 kg of top-up plus 4.5 kg of change is 10.5 kg; a generous pour and a 3 kg weekly top-up is 16 kg.
Box size changes it. A box 1.5 times the cat's body length holds 6–8 kg of clay at proper depth, so a small box does not save litter — it makes the cat dig deeper, track more and urinate over the edge.
Four litters, four densities
Price per kilo means nothing until you know how much of it leaves the bag each month. The four common types behave completely differently:
- Clumping clay, $1.00–1.55/kg (18 kg bag, $18–28). Heavy, strong clumps, 10–15 kg a month. Cheap per kilo, high mass.
- Tofu, $3.00–5.40/kg (2.4 kg bag, $9–13). Light clumps, low dust, 8–12 kg a month because the pellets are less dense and the clumps smaller.
- Pine pellets, $0.70–1.10/kg (18 kg bag, $13–20). Sawdust falls through, so the whole box is dumped weekly: 16–20 kg a month.
- Silica crystal, $3.30–6.10/kg (3.6 kg bag, $13–22). Only solids come out; 3–4 kg a month, full change every 3–4 weeks.
Which one suits a given cat — paws, dust, tracking, senior mobility — is compared in litter types compared.
Monthly and yearly, side by side
| Litter | $/kg | kg per month | Cost per month | Cost per year | Full change |
|---|---|---|---|---|---|
| Clumping clay | 1.00–1.55 | 10–15 | $12–22 | $150–260 | every 2–4 weeks |
| Tofu | 3.00–5.40 | 8–12 | $30–55 | $360–660 | every 2–3 weeks |
| Pine pellets | 0.70–1.10 | 16–20 | $12–22 | $150–260 | weekly |
| Silica crystal | 3.30–6.10 | 3–4 | $14–24 | $170–290 | every 3–4 weeks |
Two lines tie at $150–260 a year for opposite reasons. Clay is cheap per kilo and heavy in use; pine is cheapest per kilo and heaviest in use. Crystal has the highest shelf price and the lowest mass, which puts it within $30 of clay over 12 months.
Why cheap per kilo is not cheap per month
The only number that matters is kilos used per month × price per kilo. A $0.90/kg pine pellet that you dump weekly costs more than a $1.40/kg clay you top up, because the pine puts 16–20 kg through the box against 10–15. A $12 bag of clay that clumps badly and crumbles on the scoop also loses: broken clumps mean you scoop twice as often and change the box every 10 days instead of 21.
Clump strength is the hidden variable. Good clumping litter forms a firm ball in 60 seconds and lifts out whole; poor litter breaks into dirty pieces that stay in the box and smell within a week. The cost comparison that accounts for this, including the price per cleaned box, is in cheap vs expensive litter.
Two cats are not double
Two cats use 1.8–2.2 times the litter of one, not 2.0: two boxes get scooped on the same schedule but the depth is shared. Budget 18–30 kg of clay a month and $22–45, or $260–520 a year. The standard rule is one box per cat plus one, so three boxes for two cats; that third box adds 4–6 kg of litter to the first fill and roughly 15% to the monthly total.
Skipping the extra box saves $15–25 a month in litter and often costs $100–300 in enzyme cleaner and a replaced rug, which is the wrong trade.
Deodorizing is a separate line
Litter does not deodorize; airflow and removal do. Still, the add-ons cost real money: baking soda at $4–8 a month sprinkled in the bottom, carbon filter pads for a hooded box at $4–8 each and replaced monthly, liners at $0.40–0.80 each if you use them. That is $10–20 a month on top of litter — up to $240 a year, more than the litter itself in a clay-only budget.
The cheapest deodorizer is the scoop, and the second cheapest is a second box: two boxes on one cat halve the depth of urine in each and add $10–15 a month in litter, less than a carbon filter subscription. A covered box with a carbon pad traps odor but also traps ammonia when the pad is overdue.
Scented litter is the expensive version of this: a cat that dislikes the perfume urinates beside the box, and you buy litter, cleaner and eventually a new box. The routine that keeps odor down without additives is in the litter box cleaning routine.
When the cheap bag costs a vet visit
Two failure modes have real bills. A cat that refuses a dusty or heavily scented litter holds urine, and a blocked male cat is a $600–1,500 emergency that can kill within 24–48 hours. A cat that holds stool because the box is dirty or the litter is uncomfortable becomes constipated, and a $300–800 workup follows. Both start with a $10 saving.
What to watch: urinating outside the box more than twice, squatting with little output, crying in the box, or no stool for 48 hours. Any of those means a vet visit, not a litter change.
Five steps to a predictable litter bill
- Weigh one week of top-up and one full change; multiply by 4.3 for the monthly figure.
- Price the 18 kg bag, not the 5 kg bag; per-kilo cost drops 30–45%.
- Pick the litter on clump strength and dust, then compare the monthly cost, not the shelf price.
- Add the third box for a two-cat house and keep 7–10 cm depth.
- Scoop twice daily — it is the cheapest deodorizer you will ever buy.
Frequently asked
Why does my cat use 15 kg of litter a month when the bag says it lasts a month?
Bag claims usually assume one shallow box and one scooping a day. A 7–10 cm depth in a box sized 1.5 times the cat, scooped twice daily, needs 1.5–3 kg of top-up a week plus a 4–5 kg full change every 2–4 weeks. That is 10–16 kg a month. Weigh one week of top-up to see whether you are pouring more than you think.
Is crystal litter actually cheaper than clumping clay over a year?
It comes within $30 of it. Crystal costs $3.30–6.10 per kilo but one cat uses only 3–4 kg a month because you remove solids and stir, with a full change every 3–4 weeks. That is $170–290 a year against $150–260 for clay at $1.00–1.55 per kilo and 10–15 kg a month. The clay is cheaper; the crystal is lighter to carry.
How often should the whole box be emptied, not just scooped?
Every 2–4 weeks for clumping clay and tofu, weekly for pine pellets because they break down into sawdust, and every 3–4 weeks for crystal. Wash the box with unscented soap and hot water at each change, dry it fully, and refill to 7–10 cm. A box that smells after three days usually needs a full change, not more deodorizer.