Scuba Weight Calculator

Get a first guess for your lead from your body weight, suit, cylinder and water, then fine-tune it with a buoyancy check.

Results update as you type.

Quick examples

Load a full example, then change any value.

Your body weight (kg)

Without gear. Two divers of the same weight can still need different amounts.

Exposure suit

10% of body weight (DAN and PADI).

Cylinder

Luxfer figures in salt water, with valve.

Water

Gear weight without lead (kg)

Suit, BC, regulator and cylinder. Only used for the salt and fresh water difference. An empty AL80 alone weighs 14.3 kg.

Starting weight

First guess

Start with about 10 kg (22 lb) of lead, then check it in the water.

5-7 mm full wetsuit: 8 kg
AL80, empty: +2.02 kg
Starting weight: 10 kg

Carrying too much lead is common. Scuba Diving magazine calls 5 extra pounds (2.3 kg) typical. Each extra kilo needs about a litre more gas in the BC, and that gas grows and shrinks every time you change depth, so control gets harder.

AL80 during the dive

Full (207 bar)

−0.8 kg sinks

At 35 bar

+1.54 kg floats

Empty

+2.02 kg floats

Maker's figures in salt water, with valve. The starting weight covers the empty figure.

Salt and fresh water

In fresh water you need about 2.6-3.1 kg less: 2.4-2.8% of 110 kg, which is you, your gear and the lead. Start with 7 kg there.

Seawater is 1,024-1,028 kg/m³ and fresh water about 1,000 kg/m³, so the sea lifts the same volume 2.4-2.8% harder.

Buoyancy check at the surface

The number above is a starting point. This check is the real test.

1
Get into the water you will dive in, salt or fresh, in full kit with the lead on.
2
Empty the BC completely and hold a normal breath. You should float with the water at eye level.
3
Breathe out. You should sink slowly until the water is just over your head, then rise again as you breathe in.
4
Checking with a full AL80? Add 2.3 kg. That is the weight of the gas you will breathe before 35 bar is left. With about 35 bar left, no change is needed.
5
Confirm at the end of the dive: at 5 m with 35 bar left and an empty BC, you should hover without effort. Change the lead 1 kg (2 lb) at a time, and don't let a test take you below 6 m.

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These tools are educational planning aids; they are not a substitute for dive training, current printed tables or a dive computer. Verify results against your training and always plan within the limits of your certification.

About weighting

Lead cancels the lift of everything that floats: your body, your suit and, at the end of the dive, an aluminium cylinder. The right amount lets you hold a stop at 5 m with an empty BC and 35 bar left.

The published rules give a share of body weight for each suit and a fixed amount for the cylinder. They are written for salt water, so fresh water takes off about 2.5% of your total weight.

With your numbers

Enter valid values to see the calculation worked through with your numbers.

Formula

Lead in salt water

Lsalt = p × W + a + C

Lead in fresh water

Lfresh = Lsalt − f × (W + G + Lsalt)

Aluminium cylinder when empty

C = B35 + (B35 − Bfull) ÷ (Pfull − 35) × 35

Where

W: your body weight (kg)
p: 5% for a 3 mm suit, 10% for 5-7 mm and dry suits, 0 for a swimsuit
a: fixed extra for a swimsuit, hood and gloves, or a dry suit (kg)
C: cylinder buoyancy when empty in salt water (kg, negative for steel that stays heavy)
G: gear weight without lead (kg)
f: 2.4-2.8%, from seawater at 1,024-1,028 kg/m³ against 1,000 kg/m³
Bfull, B35: maker's buoyancy full and at 35 bar; Pfull: service pressure (bar)

How it's calculated

Suit share, from PADI's rule for an aluminium 80 in salt water and DAN's Alert Diver article Weight Up!: 3 mm wetsuit 5% of body weight, 5-7 mm full wetsuit 10%.
Other suits, from the PADI Peak Performance Buoyancy table published by Scuba Diving magazine: swimsuit or dive skin 0.5-2 kg; 7 mm with hood and gloves 10% plus 1.5-3 kg; shell dry suit 10% plus 1.5-3 kg (thin undergarment) or 3-7 kg (thick); neoprene dry suit 10% plus 3-5 kg.
Cylinder: its buoyancy when empty in salt water, with valve. Luxfer (AL80, AL100) and Faber (HP80, HP100) figures come from the spec sheets published by XS Scuba. Luxfer lists full and 35 bar, so the line is extended to 0 bar: an AL80 is +2.0 kg empty, the same as PADI's 2 kg allowance.
The 12 L and 15 L Faber 232 bar figures come from two Faber dealer tables (South West Rocks Dive Centre and Scuba Doctor) that differ by about 0.6 kg, so these cylinders give a range.
Fresh water: minus 2.4-2.8% of you plus gear plus lead, because seawater is 1,024-1,028 kg/m³ and fresh water about 1,000 kg/m³ (The Open University). Scuba Diving puts the difference at 4-7 lb (1.8-3.2 kg).
The result is the middle of the range, rounded to the nearest 0.5 kg and never below 0. Pounds = kg ÷ 0.45359237, rounded to a whole pound.
Full-cylinder correction for the surface check: buoyancy at 35 bar minus buoyancy full, from the same sheets (AL80: 2.3 kg). Scuba Diving gives 5 lb (2.3 kg) for a typical cylinder.
End-of-dive check from DAN: hover at 5 m with 35 bar and an empty BC, adjusting 1 kg (2 lb) at a time. PADI adds: don't go below 6 m during the test.

Good to know

Write the lead that passed the check in your log, with the suit, cylinder and water. Next time, start from that number instead of a rule of thumb.
Fat floats and muscle sinks, so a lean diver may need less than the rule and a diver with more body fat may need more. The sources give no figure for this, so the check decides.
PADI's surface check uses a full breath instead of a normal one. A full breath gives more lift, so that version tends to end with a little less lead.
Check again after any change: a new suit, a different cylinder, fresh water instead of the sea, or a change in your own weight.

How to use the scuba weight calculator

1
Enter your body weight, then pick your suit, your cylinder and the water you will dive in.
2
Read the starting weight and the breakdown. When the rules give a range, the result is its middle.
3
Do the buoyancy check at the surface, confirm it at the end of the dive and write the number in your log.

What the result means

The starting weight is a first guess from published rules of thumb. DAN and PADI both finish with an in-water check, because no rule knows your body composition, how much air you keep in your lungs or how worn your suit is.

The cylinder line can be plus or minus. An aluminium cylinder floats at the end of the dive, so it adds lead. Steel cylinders such as the HP100 stay slightly heavy when empty, so they take a little off.

If you do the surface check with a full cylinder, add the weight of the gas you will use. For an AL80 that is 2.3 kg; the check card shows the figure for your cylinder.

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