Calculate your boat's displacement and D/L ratio.
feet
feet
feet
0.35-0.60 is typical
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Download NowDisplacement is the total weight of your boat and everything in it, expressed as the weight of water the hull pushes aside to float. Archimedes' principle makes this the anchor number for the whole design: it determines draft, required sail area, engine size, stability, trailering weight, and even insurance value.
For a DIY builder, knowing your displacement before you cut timber prevents a cascade of expensive surprises. A boat that is 20% heavier than planned draws deeper, heels more, needs a bigger rig and engine, and may no longer be towable by the vehicle you own.
This calculator converts your displacement (in pounds) and waterline length into the Displacement-Length Ratio (DLR), a non-dimensional figure that tells you whether your boat behaves as light, moderate, or heavy for its size. Enter your figures above to see where your design sits.
DLR = (Displacement ÷ 2240) ÷ (LWL ÷ 100)³| DLR Range | Character | Typical Boat |
|---|---|---|
| < 100 | Ultra-light | Dinghies, skiffs, racing sleds |
| 100 - 200 | Light | Daysailers, light cruisers |
| 200 - 300 | Moderate | Most cruising sailboats |
| 300 - 400 | Heavy | Blue-water & icebreakers |
| > 400 | Very heavy | Full keels, trawlers, workboats |
Typical DLR bands for sailing and power craft.
Formula verified against standard naval-architecture references · Updated October 2026
Displacement is the weight of the boat, equal to the weight of the water it displaces when floating. By Archimedes' principle a boat that weighs 6,000 lbs pushes aside 6,000 lbs of water. It is usually quoted in pounds or long tons, and it can be measured by weighing the boat, by calculating hull volume, or by reading the draft at a known load.
For sailing boats under 30 ft, a DLR of 100 to 200 reads as light and lively, while 200 to 300 is normal cruising comfort, and above 300 indicates a heavy blue-water or workboat hull. There is no single 'good' value — the right DLR depends on mission. A daysailer wants to be light; an ocean cruiser trades speed for carrying capacity and sea-kindly motion.
The simplest accurate method is to weigh the boat or measure its draft and compute the immersed hull volume, then multiply by water density (about 62.4 lbs per cubic foot in fresh water and about 64.0 lbs per cubic foot in salt water). For planning, sum the weights of the major components — shell, deck, rig, engine, ballast, and stores — which is what most builders realistically do.
Yes. Full displacement includes everything fixed to the boat plus its useful loads: hull, deck, spars, rigging, engine, shafts, ballast keel, tanks with fluid, batteries, and gear. Builders often quote 'light ship' weight, but performance numbers like DLR and sail area to displacement should use the loaded figure you actually sail with.
Heavier displacement means more water to move, so you need more sail area to drive a sailing hull at a comfortable speed and more shaft horsepower to reach a target speed under power. Under-sizing is the classic DIY failure: a boat heavier than planned with the original rig or engine becomes underpowered, sluggish, and hard to handle in light air.
Higher DLR (a heavier boat for its length) usually gives a more sea-kindly motion, greater load-carrying capacity, and better directional stability in rough water, at the cost of speed and light-air performance. Lower DLR boats are faster and more responsive but can be tackier and pound in a seaway. Most offshore cruisers land in the moderate-to-heavy band for that reason.
Salt water is denser, so a boat displaces its weight in a smaller volume and floats higher. Fresh water is roughly 3% less dense, so the same boat sits a little deeper. For a fully submerged displacement figure the change in weight is zero — the boat always displaces its own weight — but the draft and waterline shift between the two.