How to Prepare a Whelping Box

A whelping box is a simple piece of kit that gets three things wrong more often than not: it is too small, it has no pig rails, and it goes up the day labor starts. The last one causes the most trouble, because a dog who has not settled into the box by the time she is nesting will choose somewhere of her own — the back of a wardrobe, under a bed, behind the sofa — and you will spend the whelping night moving newborn puppies out of the worst possible place. Put the box up two weeks early, feed her in it, let her sleep in it, and she will treat it as hers. This page covers dimensions, rails, heating, bedding and siting, with the numbers rather than the vague advice. Work out your timings with the free dog pregnancy calculator.

Getting the Size Right

Size is set by her body, not by the number of puppies, because the mother is the constraint.

Measure her lying fully stretched out on her side, nose to the base of the tail, then add roughly a third. That is the minimum internal length.

She must be able to lie flat in any orientation without touching a wall. A dog who cannot stretch out will lie curled against a side, which is exactly where puppies get trapped.

Width is usually the same as length or close to it, giving a square-ish box. Square is easier to build and stops her always lying along one axis.

As a rough starting point: small breeds around 30 × 30 in (75 × 75 cm), medium 36 × 36 in (90 × 90 cm), large 42 × 42 in (105 × 105 cm), giant 48 × 48 in (120 × 120 cm) or more.

Bigger is not automatically better. In a very oversized box a newborn can crawl away from the heat and the mother and chill, so there is a sensible upper limit.

If you already have her measurements from crate shopping, they transfer directly — the measuring method is the same one used in the crate size calculator.

Box Size by Dog Size

Starting points to adjust against her actual stretched length.

Side height has two jobs: keeping puppies in for the first three weeks and keeping draughts out. Once they start climbing at three to four weeks the box becomes a pen instead.

One side should be lower or removable, ideally 6 to 8 in (15 to 20 cm), so a heavily pregnant dog steps over rather than jumps. Jumping in and out of a tall box in the last week is how bruised newborns happen.

A hinged or slot-in front panel solves both problems: low while she is pregnant and nursing, raised later.

Pig Rails Are Not Optional

The single most useful feature, and the one most homemade boxes leave out.

A pig rail is a batten fixed around the inside walls, roughly 4 to 6 in (10 to 15 cm) above the floor and standing 4 to 6 in out from the wall.

Its job is to stop a puppy being crushed when the mother flops down or rolls against a side. The rail leaves a protected gap the puppy can lie in.

Overlying is a leading cause of newborn puppy deaths, and it happens with attentive, experienced mothers as much as careless ones. It is an accident of physics, not of temperament.

Scale the rail to the dog. A rail sized for a Labrador is too high to shelter a Chihuahua puppy and too low to be any use under a Great Dane.

Round off the edges or use a length of dowel or rounded batten, so there is nothing sharp at eye level for a wriggling newborn.

Rails matter most in the first two weeks, while puppies cannot move quickly out of the way, and can be removed once they are mobile and steady on their feet.

Two Weeks Early, Not Two Hours

The timing is what makes the box work at all.

Assemble it and put it in place around two weeks before the due date. Whelping from a mating date can be a week either side of the estimate, so early is safe and late is not.

Feed her in it. A few meals inside the box does more to claim it than any amount of coaxing.

Put her own bedding in it — something that already smells of her, not fresh laundry.

Let her sleep in it if she will, and do not make it a place she gets shut in, because a box that feels like confinement gets rejected.

If she is still refusing it in the final week, move it. Site beats design; a box in the quiet corner she already likes will win over a better box in the wrong room.

The pay-off comes when nesting starts. A dog who has accepted the box does her digging and shredding in it, which is exactly what you want during that phase — described in how to know your dog's labor is close.

Heating: A Warm End and a Cool End

Newborn puppies cannot regulate their own temperature for the first two to three weeks, so ambient warmth does a job their bodies cannot.

The warm end should sit around 85–90°F (29–32°C) for the first week. That is the puppy zone, not the room temperature.

Drop it by roughly 4°F (2°C) a week, reaching around 75°F (24°C) by three to four weeks as they begin thermoregulating.

Always leave a cooler end. Heat over the whole floor gives puppies nowhere to escape to, and overheating is as dangerous as chilling. Warm one third to one half of the box.

Overhead heat lamps or a heat pad under part of the floor both work. A pad must be one designed for whelping, on a low setting, with bedding between it and the puppies, and it must never cover the whole base.

Do not use an unguarded human heat pad or a hot water bottle that can leak or cool. A cooling bottle becomes a heat sink.

Read the puppies rather than the thermometer. A heap piled tightly together is cold; puppies scattered flat and panting at the edges are too warm; loosely grouped and settled is right. More on the first weeks is in newborn puppy care week by week.

Bedding and Flooring

The floor has to be safe, grippy, dry and washable, in that order.

Vet bed, or a similar synthetic fleece, is the standard choice. It wicks moisture away from the surface, gives grip for pushing legs, and washes at high temperature.

Grip genuinely matters. Slippery surfaces make puppies splay their legs and can contribute to swimmer puppy, so no bare plastic or laminate underfoot.

Use newspaper for the birth itself, several layers, then strip it all out and lay clean dry vet bed once she has settled.

Have at least three complete sets of bedding. One in use, one in the wash, one dry and ready. Whelping is wetter than you expect.

No loose blankets or towels with folds once puppies are in. A newborn can burrow underneath and be lain on or chilled.

Seal or line the base if the box is wooden, so fluid does not soak in. A wipeable liner under the vet bed makes the difference between a box you can clean and one you throw away.

Where to Put the Box

Siting decides whether she uses it, and it is worth more thought than the build.

Quiet, low-traffic, and away from the front door. Not the hallway, not the kitchen at teatime.

Warm and draught-free. Off a cold floor if possible; a sheet of insulation underneath costs nothing.

Somewhere you can see and reach her easily at 3am without disturbing the whole household. A room you can sit in comfortably for hours is the practical test.

Away from other pets and children. She will be protective, and that is normal and best not tested.

Dim rather than bright. Cover part of the box or drape one side if the room is well lit.

Get her used to the room as well as the box. A dog who has spent the last two weeks of pregnancy in that room will not want to relocate mid-labor — the wider late-pregnancy routine is in how to care for a pregnant dog.

Buying, Building or Improvising

All three work. The differences are cost, hygiene and how well they scale.

Commercial plastic whelping boxes are easy to disinfect, come with rails and adjustable sides, and are the sensible choice for anyone whelping more than one litter.

A plywood box is cheap and easy to build, but bare wood absorbs fluid and cannot be properly disinfected. Seal it or line it, and expect to replace it eventually.

A hard plastic child's paddling pool works surprisingly well for small breeds: rounded, no corners, easy to wash. It takes no pig rails, so it suits small dogs least likely to overlie.

A large cardboard box is a genuine option for a toy breed and has one real advantage — you can cut a low doorway and throw the whole thing away afterwards.

A crate is not a whelping box. No room to stretch, no rails, and a door in the wrong place.

Whatever you use, it must be washable or disposable, because it will need cleaning repeatedly across the first weeks.

What to Set Up Beside the Box

The box is half the preparation; the kit next to it is the other half.

Clean towels, more than you think — for drying puppies and swapping soaked bedding.

A gram scale and a notebook. Every puppy is weighed at birth and daily afterwards, and steady gain is the earliest sign feeding is working.

A digital thermometer and the temperature chart, since the drop below 99°F / 37.2°C is what tells you the night has arrived.

Unwaxed dental floss, blunt scissors and a bulb syringe, in case a cord needs tying or a nose needs clearing.

A small warm holding box with a covered heat source, so delivered puppies are safely out of the way while the next arrives.

The vet's day and out-of-hours numbers on paper, the address, and the X-ray puppy count — the escalation thresholds themselves are listed in signs a dog is in labor.

FAQ

How big should a whelping box be?

Measure the mother lying fully stretched, nose to tail base, and add about a third. Roughly 30 × 30 in (75 × 75 cm) for small breeds, 36 × 36 in (90 × 90 cm) for medium, 42 × 42 in (105 × 105 cm) for large and 48 in (120 cm) or more for giant breeds.

What are pig rails and do I need them?

A pig rail is a batten fixed around the inside walls, about 4 to 6 in (10 to 15 cm) off the floor and the same distance out from the wall. It gives a puppy a protected gap if the mother lies against a side, and overlying is a leading cause of newborn deaths.

When should I set up the whelping box?

About two weeks before the due date. She needs time to accept it as her own space, otherwise she will nest somewhere of her own choosing — under a bed or in a wardrobe — during labor itself.

How warm should a whelping box be?

The warm end should be around 85–90°F (29–32°C) in the first week, dropping about 4°F (2°C) weekly to roughly 75°F (24°C) by three to four weeks. Always leave a cooler end so puppies can move away from the heat source.

What bedding is best in a whelping box?

Vet bed or similar synthetic fleece over a wipeable base. It grips, wicks moisture and washes hot. Use layered newspaper for the birth itself, then swap to clean dry bedding, and avoid loose blankets a newborn could burrow under.

Can I use a crate or a paddling pool instead?

A paddling pool works well for small breeds — rounded, washable and easy to step into. A crate does not: it is too small to stretch out in, has no pig rails, and the door opening is in the wrong place.

Build It Early, Rail It, and Let Her Claim It

A good whelping box is not complicated. Make it long enough for her to lie fully stretched with room to spare, fit pig rails at a height that suits her size, keep one side low enough to step over, and warm one end to around 85–90°F (29–32°C) while leaving the other cool. Lay washable vet bed over a wipeable base, keep three sets in rotation, and site it somewhere quiet, warm and reachable in the middle of the night. Then do the part that costs nothing and matters most: put it up two weeks early, feed her in it, and let her decide it is hers. Get your timings straight with the free dog pregnancy calculator, and read what the night itself involves in what to expect when your dog gives birth.