Hello all, grateful for some advice. I have a terrier bitch due in a few weeks and I am trying to determine what size whelping box she needs. Laid down on her side she measures 22" from bum to nose! I would like pig rails too which is further confusing me on the size I require. I have seen suggestions of 30" square suiting her size but im not sure if that includes the pig rails? Many thanks in advance x

No idea about pig rails as never used. I don't like a whelping box to be too small ... as the litter grows over the first 2 weeks I split half the box for bedding and half for toiletting. Nor do I like enormous boxes. Plenty of room to move around outside the box, that's not the purpose of the box itself. From my medium size breed, I guess the length (or one side) is the length of mum lying stretched out on her side, plus some inches to spare, and the width is enough for Mum to lie stretched out on her side, legs in front times 2. At a rough guess!! That's got to be better than the other answers you've had so far

For our breed, pig rails were essential.   We made a box that had two section, the first 4 X 4, had pig rails round three sides, a gallows to hang the heat lamp from, the sides were 2.5 ft and the box had a base so it was up off the floor.   The front end of the first section was low so our low to ground girls could climb out, but not the puppies.    Once they were mobile, eyes open, we moved the box from the quiet area in the house, into the kitchen and added a second 4 X 4 section, taking the front of the first out.   That second section was similar but with no pig rails, and a hinged door at the end, access for mum - and me to get in there to clean up.   This nicely made a sleeping end and a play/emptying end.

You may not need anything as big as the one we had however!!        She should be able to be sleeping in her whelping quarters a week before whelping so her surroundings are familiar.   And you need a cot (or sofa as applicable) to sleep on with her, from the final few days, so you can keep an eye on her - and eventually, her family.