Mine came today and going on the reviews we got 36"x36" we've built it and it's huge. She's a small breed but now I'm worried it's useless.

I think as long as you can keep a heated area you should be ok.

I have a fairly large box which allows the bitch to stretch right out when she's feeding when pups are bigger. Better too big than too small so long as you can keep awarm area for pups to gravitate to and I would use the anti crush bars even if you think you won't need them.

When making one with a friend she was told by breeders in her breed if its too big it's easy for pups to get lost in it and cool down too much. The one we made ended up being too big in the end and she had that problem so we knocked up a smaller one then once the pups were bigger moved them into the bigger box.

Could you put a smaller box for the puppies in the corner under the heat lamp? Apologies if it's a stupid idea.

I have an exceptionally tiny breed.  My crate is a 4 footer.  I order brand new cardboard boxes (triple thickness) 12" x 18" x 18".
The cardboard box is great because I can burn it when it gets too soiled.  Bought in packs of ten for around £36 I've never got through a full pack. 

I know there are expensive disposable boxes available but this suits my breed.  I cover the box entirely, with enough room for mum to shove her nose out and look what's going on.  The heat pad is left on 24/7 and pups gravitate towards it when not suckling.  Mum can move away from the heat.  I let pups venture out when they are ready.  The reason I use such a large crate is for pups to safely practice standing and moving around.  I expect pups to be big enough to get over the 4" lip before they are introduced to large breeds.  This doesn't happen until 4 weeks with my breed.

Thanks guys, it's a disposable one I bought it's really quite good other than me worrying about the size. I think I will buy another say 30x30" I bought quite a large heat pad so that should help.

Very exciting! More stuff just arrived. I'm so nervous something will go wrong in the next 4 wks.

Our whelping box, based on another I'd read about consisted of a 4 X 4 section with a pig rail round three sides, with the sides about 3 ' and the front end had a lower side so mum could clamber out, but not the puppies - bearing in mind mine is a low to ground hound and with her milk-bar, the access couldn't be too high.  Ouch.   We had a brood lamp above the middle of this section and a thermometer in the base (which was off the ground) to check the temperature down there.    Once the puppies were up and moving around, we moved the box into the kitchen (it was in the living room by a sofa bed, for obvious reasons) and added a second 4 X 4 section which had a hinged door at the end for coming and going.   The low side being removed.   This gave the pups a good area, the original end being the sleeping quarters still, and the front, playing/toiletting.

Provided you have external heating where the box is (ideal is a brood lamp over it), it doesn't really matter what size as long as you have room to accommodate it.

ps   We did have to drape a sheet across the top, putting roughly 1/3rd of the area in the shade so mum wasn't lying immediately under the brood lamp and getting too warm when lying down to feed her brood.   I found the brood lamp, suspended over the box (gallows?), kept the whole area dry.

That's great thank you. I shall look into the lamps also. Think I've got all the necessary things now :-)

Please, please don't use a heat lamp.
I've bred dogs for nearly 40 years and in the beginning I made my poor dogs endure the persistent and over powering heat from a lamp.
Bless their hearts they were such good mothers they endured the heat and spent some miserable weeks being cooked.
A heat pad in a draught free room gives the mother the luxury of enjoying being with her puppies, you suddenly get better mothering skills, comfortable and quiet babies and peace of mind.

In a larger whelping box I use warm wheat filled bags ( the ones sold on Amazon in twos) ...I place them like a barrier around them keeping them close enough to the milk bar and in close proximity to the heat pad without mum having to lay on the heat. They are in a little safe lagoon if you get my meaning.

Yes I see that's a good idea! I shall just do that cause the lamp was looking difficult to put above the box anyway. Off on to amazon I go.. Again :-D

Agree, in average domestic situation, in a heated house, especially with a coated breed, a heat pad is much better.

Re a brood lamp - provided it's at the correct height, there's NOTHING WRONG with using one - and as suggested, it keeps the whole area dry at a time when with a big litter, it can get a tad 'damp'

Each to their own, I guess.     "especially with a coated breed"    I guess this is relevant - mine wasn't.

Just been digging my heat pad and bedding out from under the stairs, checking the heat pad still works, washing the bedding etc. Next job is to get the whelping box in from the garage, disinfect it all and put it together. 3 weeks to go, but I remember that box and it's fiddly, might take me a week or so to work it out! Then I just have to redesign the dining room which is the quietest part of the house for the puppies and me to sleep in for the first few weeks. :-)

Yes I'm just going with my heat pad it's quite large & I will buy some other heat bags too. Hope it's a quick few wks!!