InDesign sizes don't match up to Photoshop sizes

Hi there,

I've run into this issue a number of times and I don't know if I'm doing something wrong or if it's some quirk with InDesign. Anyway, I laid out a 1000 px x 1000 px document in InDesign to upload to a website that has size restrictions. I can't get the site to take it - even though it tells me that the maximum dimensions are 3000 px x 3000 px. I was all set to reach out to the site's help and then it occurred to me that I've had this problem before. So I opened up the same document in Photoshop to check the dimensions and Photoshop is telling me that my document is 4167 px x 4167 px. I don't understand why this is. I set my dimension in InDesign, but then when I export the document as a JPEG and check the size in Photoshop it's never the size I laid it out to be.

Why is this and how can I correct for it?

If it helps, I'm using CS6 and I'm still a novice.

Thanks!