Buoyancy & conditions / Calculator 09
Lift Bag Size & Volume Calculator
Estimate an object's submerged weight, the minimum bag displacement, and the surface gas needed to inflate it at depth.
The numbers / explained
Ready when you are.
Start with the example or enter your own numbers, then calculate.
Every result includes units. All calculations run in your browser.
01 / The calculation
How it works
Net lift = dry object weight − water density × object displacement. Bag displacement = positive net lift ÷ water density. Surface-equivalent fill gas = bag displacement × ambient pressure. Density: 63.94 lb/ft³ salt water and 62.35 lb/ft³ fresh water (1.027 and 1 kg/L).
Reference: NOAA diving formulas02 / Before you use it
Keep in mind
Theoretical static lift only. No allowance for suction, rigging, dynamic loads, bag shape or a working margin. A buoyant object needs no added lift. Gas expands on ascent; lifting requires suitable training, venting and rated equipment. Do not use this minimum as an equipment working-load rating.