To estimate monthly litter cost, divide fresh litter used by the days observed, multiply by 30.44, then multiply by the price per unit. Use the same units throughout, and include litter used for full changes as well as top-ups.
This is our calculation method, not a report of Goldfish’s consumption. The numbers below are invented to make the working visible.
1. Record what you paid for
Keep the product name, variant, pack quantity, date and receipt total. Record discounts and delivery separately, then decide the cost basis you want to compare.
If delivery is solely for the litter, include it. For a mixed order, show any delivery allocation explicitly; do not quietly charge the entire delivery fee to one product in one comparison and none in another.
Price per unit = net pack cost ÷ pack quantity. A synthetic 10kg pack costing £12 works out at £1.20 per kg, or £0.0012 per gram.
2. Measure fresh litter, not dirty waste
Record every addition to the tray. A scoop of used litter contains more than the fresh material you bought, so weighing the bin bag does not tell you how much new litter you consumed.
| Date | Fresh quantity | Reason | Notes |
|---|---|---|---|
| Each addition | Grams or measured litres | Top-up or full refill | Tray, spill, routine change |
| No addition | 0 only if checked | No fresh litter used | Do not leave an ambiguous blank |
| Missed record | Unknown | Missing observation | Recover from stock if possible |
For a steady-running estimate, begin immediately after a full refill, record that initial fill separately, and observe through the next full refill. That gives one complete cycle of top-ups and replacement. Repeat cycles if the routine varies. A short spell between full changes will underestimate ongoing use if you leave the replacements out.
3. Keep mass and volume separate
A litre measures volume; a kilogram measures mass. A 10-litre bag is not automatically a 10kg bag.
If the pack is sold in litres, measure additions in litres with a consistent method. If weighing additions, obtain the net mass for that exact pack, or weigh the fresh contents while excluding the packaging. Do not borrow a conversion from another litter.
4. Work through an example
Illustrative inputs: 2,800g of fresh litter used across a complete 14-day refill cycle; a separate initial fill excluded; a 10,000g pack costing £12 including the chosen delivery allocation. No missing days.
- Daily use: 2,800 ÷ 14 = 200g.
- Estimated monthly use: 200 × 30.44 = 6,088g.
- Price per gram: £12 ÷ 10,000 = £0.0012.
- Monthly litter cost: 6,088 × £0.0012 = £7.31, rounded to the nearest penny.
30.44 is a rounded average month length. This estimate assumes the observed routine continues. It is not a claim that a cat should use this quantity or that £7.31 is a typical bill.
5. Keep purchases and consumption in separate totals
Buying three bags this month does not mean you used three bags this month. Your cash budget records the payment when it happens; your use estimate spreads the cost of material actually consumed. Both are useful, but they answer different questions.
A stock check can help: opening unused stock + purchases − closing unused stock = material taken from storage. Account separately for spills or material used elsewhere. If you cannot reconstruct a missing quantity, mark the estimate incomplete instead of entering zero.
Put the result into your household cat budget. If you are comparing routines, read clumping versus non-clumping litter; for the wider purchase decision, see choosing cat litter.
Research guide · Sources checked 7 September 2026. Product examples illustrate the decision; they are not hands-on reviews. How we work.