Displacement Estimator (From Hull Dimensions)
Estimate a hull's displacement from LWL, beam and draft via the block-coefficient method — the naval architect's first-pass weight check.
Archimedes does the weighing: the hull displaces exactly its weight in water, so volume × density IS the displacement. The block coefficient compresses all the hull's curvature into one number — get it from a sister-ship type if unsure.
Formula
⚠️ For planning and education only — verify with your vessel's documentation, naval-architecture data and official sources. Not for navigation or stability decisions on real voyages without professional data.
Estimate a hull's displacement from LWL, beam and draft via the block-coefficient method — the naval architect's first-pass weight check.
About Displacement Estimator (From Hull Dimensions)
No scale weighs a 32-foot boat conveniently — but Archimedes does it for free: a floating hull displaces its weight in water exactly, so length × beam × draft × a fullness factor (the block coefficient) × water density yields the weight. This calculator runs the naval architect's first-pass estimate, with C_b guidance per hull type and the salt-versus-fresh density distinction that moves the answer 2.5%.
How to use Displacement Estimator (From Hull Dimensions)
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula ∇ = LWL × B_wl × T × C_b; Δ = ∇ × 64 lb/ft³ (seawater; fresh 62.4) substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Displacement Estimator (From Hull Dimensions)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula ∇ = LWL × B_wl × T × C_b; Δ = ∇ × 64 lb/ft³ (seawater; fresh 62.4) with sources cited on the page
- ✓Archimedes does the weighing: the hull displaces exactly its weight in water, so volume × density IS the displacement. The block coefficient compresses all the hull's curvature into one number — get it from a sister-ship type if unsure.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
What exactly is the block coefficient?+
The fraction of the bounding box (LWL × beam × draft) the immersed hull actually fills: a slab-sided barge fills ~0.8 of it; a wineglass-sectioned sailing yacht only ~0.35–0.45. It's the single number summarizing how 'carved away' the hull is — pick it from the type tables (this tool's hints) or back-calculate it from a documented sister ship.
Why does the draft input exclude the keel?+
The block coefficient convention measures the canoe body — the hull proper — because fins and bulbs are thin appendages contributing little volume despite lots of draft. Including a 6-ft fin keel's draft would triple the bounding box while adding maybe 2% volume, wrecking the estimate. Add keel/ballast volume separately if precision demands (it rarely does at this level).
How accurate is the method?+
Within ±10% when C_b is chosen well — entirely adequate for trailering weight sanity checks, lift-capacity bookings, or auditing a seller's optimistic brochure number. Designers refine with prismatic and midship coefficients; surveys refine with measured freeboard against the lines plan. For 'is this boat really 9,000 lb as claimed?', this page settles it.
Fresh or salt water — does it matter here?+
By 2.5%: seawater weighs ~64 lb/ft³, fresh ~62.4. The same hull floats deeper (displacing more volume, same weight) moving from sea to lake — visible on a loaded ship's Plimsoll marks, which carry separate fresh/tropical/winter lines for exactly this physics. This tool assumes salt; multiply by 0.975 for the lake version of the same waterline.
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