Weight guesstimation

[Indiana Girl]

My rest-of-the-summer gig is helping out in my local dive shop a few days a week. I'm lovin' it, that's for sure! But since I'm still kind of new to scuba (8-27-06) I have a question about weighting. Not for me, but for the divers who come in needing rental gear. I've heard that the "guesstimation" formula for the amount of weight is 10% of the diver's weight plus a few pounds, or is it more or less than that?
I realize that it's up to the diver to make sure he is properly weighted once in the water, yet I'd at least like to be able to hit somewhere close to the right amount I should send him off with when he comes in for rental gear.
Thanks, everybody!

 

[GrandpaScuba]

It depends on the particular diving environment. In Puget Sound where the water is between 42 and 55 degrees F. Students are typically put in a 7mm FJ wetsuit. With this type of equipment, we give the students 10% of their body weight plus 10lbs, if we want to spend time later to fine-tune the weight. If there won't be time or opportunity to fine-tune the weight, then we use plus 15lbs.

Whenever possible we give them a belt of 8 to 10lbs less than they actually need and put the remaining weight in integrated weight pockets on the BC, for comfort.

 

[SteveAD]

Too many variables for any formula to work. How much of the divers mass is fat, muscle, bone? what are they wearing for a suit 3mm, 5mm, 7mm, 1 piece, 2 piece, dry? Get advice from some of the "old timers" at the shop. I usually base my estimates on a persons shape rather than even asking their weight.

 

[Scuba.com]

The 10% rule is usually a good place to start. This would work for a 7mm suit used in the ocean. Buoyancy can be changed at the end of a dive up to 4lbs. using an standard aluminum 80cuft tank. Which means you'll need more weight. Steel tanks tend to be negatively buoyant and can allow the diver to use less weight anywhere from 2 to 10lbs depending on the tank.