Whether your are looking to buy a whelping box or make one for your pregnant dog, you want to consider the dog's weight and size, how many puppies she is having and her temperament. Different dogs require whelping boxes of differing sizes.
Measuring for the Whelping Box
When measuring for a dog whelping box, measure your dog when she is lying down and fully stretched out. Then add an extra foot for her measurement. If you're going to add rails or barriers along the sides, add add an additional few inches.
Dog Whelping Box Sizes
If you have a small dog, consider a whelping box that is about 21 to 34 inches long and about 21 to 34 inches deep. For medium-size dog breeds, considered a whelping box that is about 28 to 34 inches long by 28 to 34 inches deep. Large dog breeds need whelping boxes that measure about 42 to 45 inches long by 34 to 40 inches deep. Extra-large breeds need boxes at least 48 to 58 inches long by 40 to 48 inches deep.