How to Build a Whelping Box: Dimensions, Materials, and Setup

The whelping box is one of the most important pieces of equipment a breeder owns. It provides a safe, warm, contained space for the dam to whelp and nurse her litter. A well-designed whelping box prevents hypothermia, reduces crushing deaths, and gives the dam security.

Sizing Your Whelping Box

The box should be large enough for the dam to lie fully stretched out on her side, large enough to move and turn without stepping on puppies, but not so large that puppies can get stranded away from the dam.

Size Guidelines by Breed:

• Toy breeds (under 10 lbs): 24 x 24 inches minimum
• Small breeds (15-30 lbs): 36 x 36 to 36 x 48 inches
• Medium breeds (35-65 lbs): 48 x 48 inches
• Large breeds (65-100 lbs): 48 x 60 to 60 x 60 inches
• Giant breeds (100+ lbs): 60 x 72 inches or larger

Wall height: 8-12 inches for toy breeds; 12-18 inches for medium; 18-24 inches for large and giant breeds.

The Most Critical Feature: Pig Rails

The pig rail is a horizontal rail set 3-4 inches off the floor and 3-4 inches from each wall, running around the entire interior perimeter. When a dam lies down suddenly, puppies against the wall can be trapped and crushed. The pig rail creates a safe space under the rail that the puppy can escape into but the dam cannot follow.

Pig rail specifications: 3-4 inches off floor, 3-4 inches from wall, round or smooth — no sharp edges. A whelping box without a pig rail is incomplete.

Materials

Wood (Most Common DIY): 3/4 inch exterior grade plywood. Seal all interior surfaces with waterproof, non-toxic polyurethane before use. Do not use particleboard.

Plastic: Heavy-duty polyethylene. Easy to clean, does not absorb odors.

Flooring Inside the Box

Best options:

• Vetbed/Dry-Bed fleece: The gold standard. Moisture wicks through to underneath, keeping surface dry. Machine washable. Highly recommended.
• Non-slip rubber mat under Vetbed.
• Whelping pads as a base layer.

Avoid: Shredded newspaper (slippery when wet), cedar or pine shavings (respiratory irritants), terry cloth alone (puppies catch nails in loops).

Temperature Management

• Week 1: 85-90 degrees F
• Week 2: 80-85 degrees F
• Week 3: 75-80 degrees F
• Week 4: 70-75 degrees F (room temperature)

Heat sources: Heating pad under HALF the box only on LOW setting — creates thermal gradient. Heat lamp above one corner. Use both for redundancy. Monitor with a thermometer at puppy level.

Step-by-Step: Building a 48 x 48 Inch Wooden Box

1. Cut plywood: 2 side panels (48 x 18 inches), 2 end panels (48 x 18 inches), 1 floor panel (48 x 48 inches)
2. Assemble with wood screws, reinforce corners with 2x4 blocks
3. Sand all interior surfaces smooth
4. Apply 2-3 coats of waterproof sealant to all interior surfaces. Allow to cure fully.
5. Cut a low entry notch in one wall (the dam's step-over height — 6-8 inches for medium breeds)
6. Install pig rails: attach 1x4 boards or PVC pipe horizontally around interior, 3.5 inches from floor and 3.5 inches from wall

Total cost: $60-150 in materials.

When to Set Up

Set up the whelping box 2-3 weeks before the due date and introduce the dam to it. Allow her to sleep in it voluntarily. A dam who enters the box for the first time during labor may reject it and whelp somewhere else.

Summary

Size the box for the dam to lie fully stretched. Install pig rails on all interior sides. Line with non-slip Vetbed. Heat to appropriate temperature. Set up 2-3 weeks before whelping. The pig rail is the single most important safety feature — do not skip it.