Dive Planning

Dive Weighting Adjustment Calculator

Adjust a verified weighting for salt or fresh water, a different cylinder, or a gear change.

Known weighting and what changes

Start from a weighting you have verified in the water, then describe what is different. Lift added by a change is entered as positive; lift removed as negative.

Verified reference

Water

Lead that was neutral

Total mass in the water

New setup

Water

Cylinder buoyancy change

Other lift change

Where the change comes from

Water density

-2.4 kg

Cylinder

0.0 kg

Other gear

0.0 kg

Water change = total mass × (new density ÷ reference density − 1), using 1.025 kg/L for seawater and 1.000 kg/L for fresh water. The cylinder entry is the difference in buoyancy at your weight-check pressure, not a full-tank value. Suit compression and your own buoyancy are not modelled.

A starting point, not a replacement for a check

Confirm any change with a buoyancy check at the end of a dive: floating at eye level with a nearly empty cylinder and an empty BCD, then adjust. If the reference weighting was never verified, start with a check rather than this tool.

How it works

\Delta m_{\text{lead}} = M\left(\frac{\rho_{\text{new}}}{\rho_{\text{ref}}} - 1\right) + \Delta B_{\text{cyl}} + \Delta B_{\text{other}}

Where

$\Delta m_{\text{lead}}$: change in lead (kg); positive adds lead
$M$: total mass in the water at the verified weighting (kg)
$\rho$: water density: 1.025 kg/L seawater, 1.000 kg/L fresh water
$\Delta B$: change in lift from the cylinder or other gear, in the same weight unit

Worked example: 100 kg total moving from salt to fresh water gives 100 × (1.000 ÷ 1.025 − 1) = −2.44 kg, so about 2.4 kg less lead. 1 kg of lift is balanced by 1 kg of lead.

Result

3.6 kg of lead

-2.4 kg from your reference weighting. Verify in the water.

Frequently Asked Questions

Why start from a verified weighting?

How much lead you need depends on your body, suit and technique, none of which a calculator can see. A weighting you have checked in the water already contains them, so only the change needs calculating.

How much less lead do I need in fresh water?

Seawater is about 2.5% denser than fresh water, so total mass × 0.024 less lift. A 100 kg setup needs about 2.4 kg less lead in fresh water.

How do I find the cylinder buoyancy change?

Compare the buoyancy of the two cylinders at your weight-check pressure, not when full. Aluminium cylinders typically become more buoyant as they empty.

Is the result enough?

No. Confirm it with a buoyancy check: float at eye level with an empty BCD and a nearly empty cylinder, then adjust.

Related Guides

Skills & safety

Weighting and Buoyancy Control

Find a weighting that lets you hold a stop at the end of a dive, and understand why cylinders and suits change the answer.

Gas planning & consumption

Scuba Cylinders Explained: Sizes, Materials, and Buoyancy

What cylinder labels really mean, how working pressure sets the gas you carry, and why aluminum, steel, and composite cylinders behave differently in the water.

Skills & safety

Scuba Buddy Checks and Predive Safety

Turn the familiar buddy check into a practical team briefing covering gas, releases, weights, computers, route, limits, and emergencies.

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Reference Data

Reference

Scuba Cylinder Specifications

Water volume, working pressure, weight, and buoyancy for common aluminum and steel scuba cylinders.

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