I would venture to say that he is 5'10" and is 6' with boots and helmet on.
Another screen comparison would be in ESB when he was dressed as the Officer escorting Leia. He stands right behind her when she screems to Luke "It's a trap". Carrie is 5'1".
My guess would be around 6' and 165 lbs.
Here is a photo from July of 2005. I got to to a live TV Morning Show with him. He really is a nice person, he could not have been any kinder.
I am 6'1" and around 193 pounds in the photo.
The helmet in the photo is one of Sarge's Mystery Helmet.
Darren
I am 5' 11-1/2" barefoot and I'm in the middle next to Jeremy in this picture that was taken last month. I'm darn close to exactly the same height as him.
Actually, if you think about it...the shoes kind of cancels out only because side by side you are both wearing shoes So to imagine a helmet to the height would add very little...IMO...only because the helmet is really not that thick to be that much of a factor. All that said, if Jeremy's 6' then he would be 6' and a hair in costume
I could be wrong in this assessment but its the best that I can do to speculate on this.
Don't know if this will help but here's a pic of both Herry [SE] and me [ROTJ] with BM's helm. I'm not too sure about Herry but I'm 5'5" and on the right.