Whelping Box Size Calculator
This calculator provides general sizing guidance based on dam weight and breed size group. Individual dogs vary — measure your dam lying stretched out to confirm dimensions. Always consult with your veterinarian or an experienced breeder mentor before whelping.
Whelping Box Setup Guide
The whelping box is the single most important piece of gear you set up for a litter. Get it right and puppies stay contained, warm, and safe from accidental crushing.
The dam needs room to stretch out, nurse, and turn around without stepping on a neonate — but not so much room that newborns can crawl away from the heat. The calculator above sizes the box from her weight; this guide covers everything else.
The short version
- Sizing: Length ≈ twice the dam's body length; width ≈ 75% of the length. Big enough to stretch out, small enough to keep newborns near warmth.
- Pig rail: A 4–6″ anti-crush rail around the inside perimeter stops the dam from pinning a puppy against the wall.
- Setup timing: Introduce the box about 2 weeks before the due date (≈ day 49–50) so the dam settles in before labor.
- Temperature: One warm zone at 85–90°F in week 1, cooling to room temperature by week 4 — never heat the whole floor.
How big should a whelping box be?
Aim for a length of roughly twice the dam's body length (nose to tail base) and a width about 75% of that length. That gives her space to lie fully stretched out and turn around while keeping the litter close.
Wall height should clear her shoulders so she can step out without climbing — but stay low enough that puppies can't tumble over the edge in the early weeks. The calculator works all of this out from your dam's weight and size group.
The sizing rule of thumb
Width runs about 75% of the length — enough for the dam to stretch and turn, no more
Choosing a box material
The best whelping box materials are non-porous, easy to sanitize, and sturdy. Here's how the three common options compare:
| Material | Best for | Pig rail | Notes |
|---|---|---|---|
| Laminated / painted plywood | Serious & repeat breeders | Easy to add | Sturdy, sealable, bleach-safe; custom dimensions |
| Plastic wading pool | Toy & small breeds | None — DIY needed | Cheap and light, but low walls; outgrown by ~week 3 |
| Commercial pen / X-pen insert | Any size, modular | Often built-in | Expandable as the litter grows; removable floor tray |
Whatever you choose, avoid untreated wood — it soaks up fluids and harbors bacteria. Seal wooden boxes with a non-toxic, waterproof coating and line the floor with washable pads.
Why the pig rail matters
A pig rail (also called a crush bar or anti-crush rail) is a horizontal ledge running around the inside perimeter, set 4–6 inches off the floor and 3–4 inches out from the wall.
Neonates can't move fast or cry loudly enough to warn the dam when she shifts. The rail creates a sheltered gap a puppy can retreat into if she rolls against the wall. Skip it and the risk of accidental suffocation climbs — especially in large and giant breeds, where the dam's weight is fatal to a newborn.
When to set up the box
Introduce the whelping box about 2 weeks before the due date — around day 49–50 of pregnancy. The dam needs time to explore it and claim it as a safe den before labor begins.
Place it in a quiet, warm, draft-free spot and add familiar bedding so she'll sleep there. Most dams start nesting in the box on their own as labor approaches. Use your whelping date calculator results to time the setup.
Set up ~2 weeks early
Early setup lets the dam settle in, so she whelps in the box instead of your closet
Bedding and floor padding
Line the floor with washable whelping pads, fleece, or newspaper (first day only). Avoid looped towels — puppy claws snag in the loops and can injure a leg.
Change bedding often during the first week when fluids are heaviest. A waterproof mattress pad under the whelping pad protects the box floor and makes cleanup faster.
Temperature control
Newborn puppies can't regulate their body temperature for the first 2 weeks, so ambient warmth is critical — hypothermia is the fastest neonatal killer. Step the box temperature down each week:
| Puppy age | Box temperature |
|---|---|
| Week 1 | 85–90°F (29–32°C) |
| Week 2 | 80–85°F (27–29°C) |
| Week 3 | 75–80°F (24–27°C) |
| Week 4+ | Normal room temperature |
Heat one side of the box — a heat lamp to one corner (never directly overhead) or a pad under half the floor — so puppies can crawl toward warmth or away from it. Keep a thermometer in the box.
Whelping box setup
Temperature Zones
Uneven heating lets puppies self-regulate. Reduce heat source gradually as they grow.
Cleaning between litters
Most breeders reuse the same box for years. Once the litter moves on, scrub it with a veterinary disinfectant or dilute bleach (1:32), rinse, and let it air-dry completely before storing.
Inspect for damage before the next litter — chewed edges, splintered wood, or a cracked pig rail should be repaired or replaced, and any porous materials that absorbed fluids swapped out.
Whelping Box FAQs
1How big should a whelping box be?
A whelping box should be large enough for the dam to lie fully stretched out and turn around comfortably, while small enough that newborn puppies cannot crawl far from warmth. As a general rule, the length should be about twice the dam's body length, and the width about 75% of the length. Use our calculator above to get specific dimensions based on your dam's weight and breed size.
2When should I set up a whelping box?
Set up the whelping box at least 2 weeks before the expected due date — ideally around day 49–50 of pregnancy. This gives the dam time to explore and become comfortable with the space before labor begins. Place it in a quiet, warm area of the house away from heavy foot traffic. Many dams will start nesting in the box on their own once they feel safe there.
3What is a pig rail on a whelping box?
A pig rail (also called a crush bar or anti-crush rail) is a horizontal ledge installed around the inside perimeter of the whelping box, typically 4–6 inches from the floor and 3–4 inches from the wall. Its purpose is to prevent the dam from accidentally crushing a puppy against the wall. Puppies can shelter under the rail, creating a safe gap between the wall and the dam's body.
4What material is best for a whelping box?
The best whelping box materials are non-porous, easy to sanitize, and sturdy. Laminated plywood and PVC-coated boards are popular among experienced breeders because they resist moisture and can be bleach-cleaned between litters. Plastic wading pools work for small breeds but lack pig rails. Avoid untreated wood — it absorbs fluids and harbors bacteria. Whatever material you choose, line the floor with washable whelping pads or fleece.
5How long do puppies stay in the whelping box?
Puppies typically stay in the whelping box for the first 3–4 weeks of life. Around weeks 3–4, when they begin walking confidently and showing curiosity beyond the box, transition them to a larger puppy pen with the whelping box still accessible as a sleeping area. By 5–6 weeks most litters have outgrown the box entirely and need a full puppy-proofed area for socialization, weaning, and play. Toy breeds may use the box slightly longer; large and giant breeds outgrow it faster.
6Can I use a child's plastic pool as a whelping box?
A hard plastic kiddie pool can work for toy and small breeds (under about 25 lb). It's easy to clean and inexpensive. The downsides: no pig rail, walls are usually too short to contain puppies past 3 weeks, and the round shape gives the dam less corner space to back into. For medium breeds and up, a kiddie pool is too small and unsafe — the dam can crush puppies against the unbarriered wall. If using one for a small breed, add a DIY pig rail with PVC pipe and plan to transition to a larger pen by week 3.
7What temperature should the whelping box be kept at?
Newborn puppies cannot regulate their body temperature for the first 2 weeks, so ambient warmth is critical. Keep the whelping box area at 85–90°F (29–32°C) for the first week, 80–85°F (27–29°C) for week 2, and 75–80°F (24–27°C) for week 3. After week 3, normal room temperature is fine. Use a heat lamp positioned to one side or a heating pad under half the box — never the whole floor — so puppies can move away from heat if they overheat. Hypothermia is the fastest neonatal killer; keep a thermometer in the box.
8Can I reuse a whelping box for multiple litters?
Yes — most breeders reuse the same whelping box for years. Between litters, scrub thoroughly with a veterinary disinfectant or 1:32 dilute bleach solution, rinse, and let it air-dry completely before storing. Inspect for damage: chewed edges, splintered wood, cracked pig rails, or worn sealant should be repaired before the next litter. Replace any porous materials (untreated wood, fabric inserts) that absorb fluids. Plastic and laminated surfaces are easiest to keep sanitary across multiple uses.