Words vs pages

I'm writing my WIP in Word, and I'm currently on page 291 (and 72,371 words). Everytime I finish a chapter, I copy it into Scrivener, partly for back-up in case Word goes wonky, partly for when I start revising (it makes it easier to swap chapters around, make notes and see the bigger picture). When I was doing NaNo, I came to terms with the fact that word counts are different between the two programmes, but was excited that the Scrivener word count also includes a 'Paperback Page Count'. I had been getting a little bit frustrated by this page count - it wasn't going up anywhere near as quickly as I had expected/hoped it would, despite my growing word count. When I realised that it was saying 177 pages for around 69,000 words, I decided to do the maths, and found that it must be using about 390 words per page to calculate the number of paperback pages your wordcount would fill. Is it just me, or does this seem a lot? I would have expected 300-350, but might be way off...