There's no calculation as people and undersuits, the two determining
factors, are so variable. I'm going to guess 12Kgs but I could be miles out.
Have at least 15 available. Getting in a pool is ideal. Then add 3Kgs for
the sea.

Sorry
nigelH

No-one can be sure. I have a small reminder which I take with me which I use
to add or subtrack Kgs of lead according to whether I use a 3mm suit, a dry
suit, am in fresh or sea water, whether I have a 3L pony or not etc etc.
What applies to me does not apply to you, but if I were to use 6kg in the
Red Sea with a 3mm shorty I would be using 10kg in a dry suit in the N Sea,
allowing for a change from Alu cylinders abroad to steel cylinders in the
UK. BTW don't get hung up about the cylinder size - broadly speaking a 15L
cylinder displaces 3L more than a 12L and so gets 3kg more lift but it also
weighs 3Kg more, cancelling this out. Of course this doesn't apply to ALL
cylinder combinations!

You'll have to be prepared to add and subtract a bit when doing it for real.
One calculation which does work is to weight yourself correctly in fresh
water (pool?). Then add up all the weights of all your kit including your
weight belt PLUS yourself, as when ready to jump in. Add 2.5% as extra lead
for the sea.

Ken

The PADI formula is:

5% of bodyweight for 3mm shorty
10% of your bodyweight plus 3-7kg (7-14)  (With chunky undersuit)
10% of your bodyweight plus 1.5 - 3kg (With thin non foa undersuit)

+  saltwater conversion
100-125 lbs bodyweight     add   2 kg
187-225 lbs     add   3.2kg
(prorata in between)

+ aluminium tank conversion
add 1-2 kg
(steel are heavier)

As we don't know your bodyweight I suggest you calculate the formula for
shorty and aluminium and see how it compares to the 6 kg you used.

Then calculate using drysuit and steel and adjust by the percentage the
first was wrong.

As a rule of thumb, we dress OW students in exactly what you will be
wearing, and the 'average' perfect weight is around 7kg (14llbs).
(The more rotund the student the more weight required usually).

Sounds like trial and error to me.  As a 50+ female, and looking through my
log books, I see the following:  Diving Stoney Cove (cold lake U.K.)  in dry
suit:  34 lbs  (could hardly haul myself onto the raft afterwards).
Caribbean, swim suit only: 12 lbs.  Fiji, wet suit:  15-18 lbs.   Costa Rica
, wet suit 22 lbs.  Maldives, wet suit:  18 lbs.  Grand Cayman:  wet suit,
15 lbs.  Havana:  wet suit, 14 lbs.

So you just gotta try it out and see.

someone