Purrify case studies cover a small apartment, a multi-cat house and a senior cat, which each need a different amount and a different bag. This page walks through all three: how much to use and how long a bag lasts.
What to do when the litter box shares a room with the bed and the sofa.

In a studio there is nowhere for the smell to go. The box sits in the same air you sleep and eat in, so the hours between scoops are the whole problem.
Purrify goes into the litter you already buy. Keep the brand, keep the box where it is, and change only the additive step.
Activated carbon adsorbs odor molecules, including the ammonia that urine releases as it breaks down, instead of covering them with fragrance. It does not replace scooping, and it does nothing about waste you have not removed.
In a small space the box is never far from you, so the hours between scoops are the whole problem.
The Large is our everyday choice for most homes, even with one cat. The everyday choice for most homes, including one-cat homes. Start on the Trial if you want to see it work first: One box, once. See if it works for you.
What changes when four cats share three litter stations in a house with children.

More cats means more waste per day and more boxes to keep on top of. Odor drifts between rooms, and perfumed deodorizers are the last thing most parents want around children.
The dose is per box, not per house. Three boxes need three doses, and the bag runs out three times as fast.
Purrify, the most powerful odor remover in the world, is fragrance-free, so it adds no scent of its own to a house with children in it. It works on the odor left between cleanings; it does not let you clean less often.
The dose is per box, not per house. Three boxes means three doses and a bag that empties three times as fast.
Several cats and several boxes is the Large case. The everyday choice for most homes, including one-cat homes.
Why an unscented additive matters more than a strong one when a cat has a sensitive airway.

Scented litters and air fresheners put fragrance into the air a cat breathes at close range, every time it uses the box. For an older cat or one with a sensitive airway, that is the part to remove.
Purrify is unscented activated carbon, so it adds odor capture without adding anything to smell. Introduce it the way you would introduce any change to a cat that does not like change.
The additive adds no fragrance of its own. It is not a treatment for anything: a sudden change in urine smell is a reason to call a vet, not a reason to buy an additive.
For a cat with a sensitive airway, the fragrance is the part to remove, not the part to increase.
One cat and one box usually starts on the Medium. One cat and a box you barely notice. The Trial is there to test the idea first: One box, once. See if it works for you.
Start with the 15g trial and see how an activated carbon additive fits into your litter routine. The bag is free and you pay shipping.