Dock Float Calculator: flotation, freeboard, and how many floats you need

How this dock float calculator works

Flotation is statics. Each float's listed buoyancy is what it supports at full submersion; your dock's capacity is float count × that number. Draft rises linearly with load: draft = float height × load ÷ capacity. The dead-load case carries the structure and the floats themselves; the live-load case adds the specified load, live load psf × deck area, on top.

The datum is where most flotation checks silently go wrong. Specs and bid packages state freeboard to the top of the walking deck. A naive check measures it to the top of the float instead, which drops the entire frame-and-deck stack sitting on the float. The error equals your frame height exactly, often 8–10 inches, which is the difference between a dock that passes its spec and one that does not. This calculator reports both datums, labeled, so you can see the gap yourself.

No datasheet handy? The tool estimates buoyancy from displacement: L × W × H × 62.4 lb/cf minus float weight, with a 10% allowance for wall and foam. Use the manufacturer's listed number whenever you have it; the estimate is for early sizing, not the sealed design. Every flotation-critical value in a real bid package (live load, required freeboard, float family) belongs to the project spec, and the spec governs.

One more habit worth stealing from good estimators: check the submerged-float case. A tall deck stack can show positive deck-top freeboard while the float itself is fully under water, which means the dock is riding on reserve it does not have. The tool flags it.