Buoyancy Calculator

What it is

The Buoyancy Calculator estimates how much lead you need to be neutrally buoyant at the end of a dive, when your cylinder is near empty and your wetsuit has lost some lift at depth. You describe your rig (water, cylinders, exposure suit, wing, and gear) and the tool adds up every buoyancy contribution to recommend a weight adjustment.

Its real strength is comparison. Change one thing, say swap an aluminium cylinder for steel or move from a 5 mm wetsuit to a drysuit, and watch how your weighting shifts. The app shows a persistent “Comparison Tool” banner at the top to make this clear: it reports how your weighting changes between setups, not an exact weighting figure. Use the relative change to plan, then confirm the exact number in the water.

How to use it

Open the calculator

From the Plan tab, open Buoyancy Calculator.

Set the water

In Environment, pick your water type: Fresh Water, EN13319, Salt Water, or Red Sea. EN13319 is the EN 13319 reference density (1.02 kg/L) that most dive computers assume, and it is the default. Saltier water floats you more, so you carry more lead in the Red Sea than in a freshwater quarry.

Add your cylinders

In Cylinders, tap a preset (Single, Twinset, Sidemount, or Stage). Tap a cylinder to open its sheet and set the shell (from the built-in database or custom), regulator type, rigging hardware, gas mix, fill pressure, and any cylinder lead.

Set your exposure suit

In Exposure Protection, choose None, Wetsuit, or Drysuit. For a wetsuit, enter the thickness, neoprene type (Soft / New, Standard, or Old / Worn), and cut, plus optional hood, gloves, booties, and vest. For a drysuit, pick an undersuit weight or a custom lift value.

Add wing and gear

Enter your wing lift capacity in Buoyancy Control, then add backplate, fins, lights, lead, and other items in Gear. An SMB and lift bag live under a collapsible Emergency section in Buoyancy Control; they do not change your weighting and are only checked against the failure scenarios. Mark anything droppable as ditchable so the failure scenarios are accurate.

Add your body, then read the recommendation

In Body & Personal Buoyancy, optionally add height and weight and a personal buoyancy offset. The Results section then shows how much weight to add or remove, any advisories, and the end-of-dive and start-of-dive analysis.

Inputs and outputs

Every input feeds one combined buoyancy sum. The main ones:

Input	What it does	Notes
Water type	Sets water density	Fresh 1.0, EN13319 1.02, Salt 1.03, Red Sea 1.035 kg/L
Target depth	Drives wetsuit compression and the start-of-dive phase	Deeper means a wetsuit loses more lift
Cylinders	Shell, regulator, rigging, gas mass, and cylinder lead	Picks shells from the cylinder database
Exposure Protection	Wetsuit (thickness, neoprene type, cut, accessories) or drysuit (undersuit)	“None” for tropical skins
Buoyancy control	Wing lift, redundant bladder, and an Emergency section (SMB, lift bag)	SMB and lift bag do not change weighting; they feed the failure scenarios
Gear	Each weight item, with a ditchable flag	Negative items sink, positive items float
Body & personal buoyancy	Height and weight, plus a measured or estimated personal offset	Optional; blank uses a simple estimate

The outputs:

Weight recommendation: how much lead to add or remove for a neutral end-of-dive, rounded to the nearest 0.5 kg. When you are already within 0.5 kg it reads “perfectly weighted”. For a drysuit, a separate ditch-weight figure appears for the flood-recovery case.
Phase results: an End of Dive and a Start of Dive card, each with a pass, warning, or fail status.
Failure scenarios: which cards you see depends on your rig. “If Wing Fails” is always shown. “If Drysuit Floods” appears only when your exposure suit is a drysuit. “If You Lose a Stage” appears only when you have a stage cylinder. Each shows whether you can still hold a stop or reach the surface.
Advisories: shown only when relevant, such as marginal wing lift, wetsuit corking risk, or overweighting.

Personal buoyancy: measured vs estimated

Your own body has a buoyancy offset, and it matters. You can enter it two ways. Measured takes the result of an in-water weight check (float at eye level with an empty BCD and a near-empty cylinder, holding a normal breath) along with the water type you measured it in, which the tool converts automatically. Estimate computes an offset from the height and weight in this section plus your age and sex, for divers who have not done a float test yet. You can add body fat percentage too; if you leave it blank the tool infers it from your BMI. Measured is always more accurate.

Behaviour and limits

Neoprene loses buoyancy as it compresses under pressure. The calculator models this with a depth-aware compression curve set by your neoprene type (soft, standard, or old), which is why a wetsuit that is comfortably buoyant at the surface can leave you heavy at depth and light again on a near-empty cylinder at the safety stop. The end-of-dive phase is the one the weight recommendation targets, because that is when you are lightest and most likely to struggle to hold a stop.

A few things to keep in mind:

The numbers are estimates from your inputs. A wrong cylinder, suit thickness, or water type changes the answer.
The tool does not know your exact undergarment loft or how much air you trap, so treat drysuit lift as approximate.
The failure scenarios assume the ditchable flags you set are correct. Double-check what you can actually drop in the water.

Deco Planner plans the decompression schedule for the dives you are weighting for.
Further reading lists the body-composition and suit-lift sources the estimator is built from, and the community calculators it is cross-checked against.

Parts of this guide were drafted with AI assistance and may contain mistakes. It's educational, not a substitute for training. Always dive within your certification and verify with your instruments.