A whelping box — queening box, if you prefer the British term — has three jobs: keep newborns warm, stop them wandering, and let the mother get in and out without stepping on anyone. Newborns cannot regulate their own temperature for two to three weeks, cannot climb and cannot right themselves, so the box is simply a heated, escape-proof, washable container. Add a fourth requirement that people forget: you must be able to reach in at 3 a.m. without dismantling anything.
Size and shape
The queen must be able to lie fully stretched out with kittens beside her, not curled around them. Measure her from nose to the base of the tail and add 15 cm for the internal length; for a typical 4 kg queen that lands around 60 by 45 cm, and 75 by 60 cm is a better working size. Bigger is not better past a point — a box so large that newborns can roll away from the heat and out of reach is a hazard, not a luxury.
Walls should be 30 to 40 cm high: too high to climb at three weeks, low enough for the queen to step over. Cut a 10 to 15 cm doorway — kittens can clear 10 cm at about four weeks, exactly when you want them contained.
Choosing the material
A large plastic storage tub is the cheapest good answer: it disinfects, it is light, and it has no joints for fluid to sit in. Cut the doorway with a craft knife and sand the edge. Plywood is warmer and looks better in a living room, but it needs sealing, because milk, urine and placental fluid soak into bare timber and stay there.
Cardboard works for one litter. Do not use anything with a lid that closes, a mesh-lined laundry basket, or a deep-pile carpet offcut — kitten claws snag, and a snag can mean a torn toe.
Bedding: the two-layer system
Layer one is disposable: newspaper or, better, puppy-training pads. Layer two is a taut, close-woven fabric — fleece, old sheets, thin towels — tucked firmly under the pad so it cannot bunch. The tautness matters. Loose bedding is how a newborn ends up underneath three siblings, cold and unfound.
Skip deep fluffy bedding and anything with loose threads, frayed hems or long pile: a single strand wrapped round a toe can cut off circulation within hours. Have six to eight spare sets ready.
Heat: the part people get wrong
Aim for 27 to 29°C in the nest during the first week, dropping to around 24 to 26°C by the third, with the room itself at 22 to 24°C. Crucially, heat only half the box. The other half must be cool enough that kittens can crawl away when they are too warm, and the mother — who runs hotter than usual and will be lying against them for hours — has somewhere to escape to.
Use a pet-rated heat mat on its lowest setting, under the box or beneath a towel on one side only, with the cable routed outside and away from teeth. Microwaveable wheat bags wrapped in a towel work well for the first night. Test the surface with the back of your wrist: uncomfortably warm after thirty seconds is too hot for a newborn.
Where to put it
The quietest room in the house, out of draughts and out of direct sun, away from the washing machine, the front door and any dog. A spare bedroom or a large cupboard is ideal. Cats want a den with a roof, so drape a towel over two-thirds of the top, leaving one side open for air.
Put a shallow litter tray and a bowl of water within a metre; for the first day or two she may not want to leave at all. Food goes slightly further away, or she will knock it over.
Timing, and getting her to accept it
Set the box up ten to fourteen days before the due date, in its final position, with bedding she has already slept on. Sit beside it for a few minutes a day so it becomes part of the furniture rather than a strange object that appeared the night she went into labour. Some queens move in immediately; others ignore it until the last twelve hours and then use it without complaint.
If she chooses a wardrobe instead, do not fight her: put the box where she has decided to nest. A queen who gives birth where she feels safe is easier to help than one relocated mid-labour.
The kit to keep beside it
Six towels, a stack of pads, blunt scissors, unwaxed dental floss, a bulb syringe, chlorhexidine or iodine for the navels, disposable gloves, a kitchen scale that reads to one gram, and a notebook. The scale is the important one: newborn weight is the best measure of whether things are going well, and a kitten should gain roughly 10 g a day after the first 24 hours.
Cleaning between litters
Wash washable bedding at 60°C, and change soiled pads twice a day in the first week. For the box itself, diluted household bleach at one part to 32 parts water, then rinse thoroughly and dry completely in the sun — chlorine and moisture are both irritants to newborns. Never use pine-based or phenolic disinfectants such as Dettol, and never use essential oils; cats cannot metabolise phenols and the toxicity is real.
If you are reusing a box, scrub it even if it looks clean: feline coronavirus, the virus behind FIP, survives on hard surfaces.
This is general information, not veterinary advice. If a queen is straining without producing a kitten, contact a veterinarian immediately.
Frequently asked
Can I just use a cardboard box?
For one litter, yes, provided it is sturdy, has a 10 to 15 cm doorway cut in one side, and you accept that it will be soaked within days and thrown away. Cardboard absorbs fluid and cannot be properly disinfected, so it never does a second litter. A plastic storage tub costs about the same and lasts for years.
How warm should the room be?
The room at 22 to 24°C, and the nest itself at 27 to 29°C for the first week, easing to 24 to 26°C by the third week. Heat only one half of the box so kittens can move off the warm spot and the queen has a cooler corner. If every kitten is piled in one tight heap and crying, they are cold; if they are spread out with limbs flung wide, they are too warm.
My cat refuses to use the box and has picked a cupboard. What now?
Let her have the cupboard. A queen chooses a nest because it feels safe, and moving her at the last minute is more likely to delay labour than to help. Put bedding down where she has chosen, keep the area quiet, and put a second box nearby. If the space is genuinely unsuitable, move the box into it rather than moving her out.