Room size and how many pets are in it — that is all we need. You get the CADR to look for, which is the number that actually decides whether a purifier works, plus the filter details that never make it onto the box.
What size air purifier do you need?
The number to match is CADR — clean air delivery rate, in cubic metres per hour. It is not room area, and it is not the “covers up to 60 m²” line on the box. Find your room below. These figures assume a ceiling of 2.4 m.
| Room area | Room volume | Light load4 air changes/h | Moderate load6 air changes/h | Heavy load8 air changes/h |
|---|---|---|---|---|
| 10 m² | 24 m³ | 100 m³/h | 150 m³/h | 200 m³/h |
| 15 m² | 36 m³ | 150 m³/h | 220 m³/h | 290 m³/h |
| 20 m² | 48 m³ | 200 m³/h | 290 m³/h | 390 m³/h |
| 25 m² | 60 m³ | 240 m³/h | 360 m³/h | 480 m³/h |
| 30 m² | 72 m³ | 290 m³/h | 440 m³/h | 580 m³/h |
| 40 m² | 96 m³ | 390 m³/h | 580 m³/h | 770 m³/h |
| 50 m² | 120 m³ | 480 m³/h | 720 m³/h | 960 m³/h |
Required CADR (m³/h) = room volume × air changes per hour. One pace of room air per hour is not enough in a pet home — the figures above already assume several.
Then add 40% before you buy
CADR is measured in a sealed test chamber with a brand-new filter. A real room has furniture blocking airflow, gaps around doors, and a filter that has already been running for months. Measured performance in a home lands at roughly 70% of the lab figure, so the number on the box needs to be about 43% higher than the number you calculated.
| Load | Air changes per hour | What counts as this |
|---|---|---|
| Light load | 4× | A short-haired pet, or a room the pet only passes through. |
| Moderate load | 6× | One shedding pet, or a litter box sitting in the room. |
| Heavy load | 8× | Several pets, more than one litter box, or odour that comes back within hours. |
The units differ by market. US and some international brands quote CADR in CFM: 1 CFM = 1.699 m³/h. Comparing a CFM figure against an m³/h requirement without converting is the most common way people buy a unit that is far too small.
Four things pet owners are not told
| Point | Why it matters with pets |
|---|---|
| Ammonia is a gas, not a particle | Litter box odour is ammonia, and particle CADR does nothing for it. What removes it is the weight of the activated carbon — aim for 2.0 kg if a box is in the room. Judge the carbon by weight, never by how many filter layers the packaging lists. |
| Turn ionisers and plasma settings off | These functions generate ozone while running. The US EPA advises against ozone generators in occupied spaces, and pets breathe faster than people, so the same concentration reaches more of their lung tissue. Turning the function off does not reduce particle or odour filtration. |
| Halve the filter replacement interval | A 12-month HEPA claim assumes a pet-free home. One shedding pet brings it to about 6 months. Carbon beside a litter box is finished long before the HEPA is. Price the filters before you choose the machine. |
| Position beats power | A purifier cleans the air that reaches it. Beside the litter box or the pet’s bed, it does far more than a bigger unit in the corner behind a sofa. |
CADR figures come from the AHAM test method; air change rates follow residential guidance from the US EPA. This page gives you a specification to shop against — it does not recommend a brand or a model.
Why CADR and not room size
Every listing advertises “covers up to 60 m²”. That line is marketing, not engineering — it is usually derived from running the machine at full speed in a sealed room. CADR is the measurement that matters: cubic metres of clean air delivered per hour, tested to a published standard. Two units with the same room-area claim can differ by a factor of three in CADR, and only one of them will clear a room with a cat litter box in it.
Then there is the gap between the lab and your living room. CADR is measured with a brand-new filter in a sealed chamber. Add furniture, door gaps and a filter that has been running for months, and you get roughly seven tenths of the figure on the box. That is why the calculated need and the number to shop for are different on this page.
The part that has nothing to do with particles
Litter box smell is ammonia, and ammonia is a gas. A HEPA filter is a physical mesh — a gas passes straight through it. What removes ammonia is activated carbon, and what matters is how much of it there is, by weight. Plenty of units marketed for pets carry a few hundred grams, which is saturated in weeks. The weight of the carbon, not the number of filter layers, is the number to check.
What we will not do
We will not name a model. Specifications do not go out of date; products do. What this page gives you is the number to match, the filter grade to look for and the consumable cost to expect — and then the decision is yours, made against real specifications rather than a “pet-friendly” badge.