Thanks Maxmixiv,

I hadn't seen the little 'like' button before, I think I need to get better glasses...
I like the alternative sentences here, I did wonder about maybe expressing that using размер, so it's good to know that this would perfectly normal for a native speaker. Приблизительно is a word I don't think I've actually used before, but it sounds pretty versatile. I feel like I'm prety on top of the subject now!

R