Hull Volume Calculator
Calculate the estimated volume of a boat hull from its length, beam, draft, and block coefficient. Convert dimensions between feet and meters and calculate hull volume in cubic meters, cubic feet, liters, and US gallons.
Hull Volume Results
What is hull volume?
Hull volume is the approximate three-dimensional volume occupied by the underwater portion of a boat or ship's hull at a specified draft. It is useful for estimating displacement, buoyancy, loading characteristics, and other naval architecture calculations.
Because a hull is normally curved and tapered rather than rectangular, its volume cannot be calculated accurately by simply multiplying length, beam, and draft. The block coefficient provides a correction for the shape of the hull.
What is the hull volume formula?
$$V = L \times B \times T \times C_b$$
$$V = Length \times Beam \times Draft \times Block\ Coefficient$$
Where:
V = estimated underwater hull volume
L = hull length
B = maximum beam
T = draft
Cb = block coefficient
How do you calculate hull volume?
First multiply the hull length by its maximum beam and draft. This produces the volume of a rectangular box surrounding the underwater portion of the hull.
$$V_{box} = L \times B \times T$$
The block coefficient is then applied to account for the fact that the actual hull occupies only a fraction of this rectangular volume.
$$V_{hull} = V_{box} \times C_b$$
Example hull volume calculation
Suppose a boat has:
Length = 30 ft
Beam = 10 ft
Draft = 4 ft
Block coefficient = 0.55
First calculate the equivalent rectangular volume:
$$V_{box} = 30 \times 10 \times 4 = 1,200\ ft^3$$
Then apply the block coefficient:
$$V_{hull} = 1,200 \times 0.55 = 660\ ft^3$$
Therefore, the estimated underwater hull volume is approximately 660 ft³, or about 18.69 m³.
What is the block coefficient?
The block coefficient, commonly written as Cb, describes how full or fine the underwater hull is compared with a rectangular block having the same length, beam, and draft.
$$C_b = \frac{V} {L \times B \times T}$$
A coefficient of 1.00 would mean the hull occupied the entire rectangular block. Real boat hulls have coefficients below 1.00 because their bows, sterns, bottom, and sides are shaped and tapered.
What does a low block coefficient mean?
A low block coefficient indicates a relatively fine or slender underwater hull. Such hulls generally have considerably less volume than a rectangular box with the same principal dimensions.
The exact coefficient depends on hull design and vessel type, so a generic value should only be used for an estimate.
What does a high block coefficient mean?
A higher block coefficient indicates a fuller hull. Cargo vessels, barges, and other vessels designed to carry large loads can have substantially fuller underwater forms than fast or slender boats.
What is the difference between hull volume and displacement?
Hull volume and displacement are closely related, but they are not exactly the same measurement.
Hull volume is a volume, normally expressed in cubic meters or cubic feet. Displacement is the mass or weight of water displaced by the underwater hull.
$$Displaced\ Mass = Hull\ Volume \times Water\ Density$$
$$Displacement\ Weight = Hull\ Volume \times Water\ Density \times g$$
In fresh water, one cubic meter of displaced water has a mass of approximately 1,000 kg. Seawater is denser, so the corresponding mass is higher.
Can hull volume be used to calculate displacement?
Yes. If the underwater hull volume at a particular draft is known, it can be multiplied by the density of the surrounding water to estimate the mass of displaced water.
$$Displacement = V \times \rho$$
For seawater, a commonly used approximate density is around 1,025 kg/m³. The actual density varies with salinity and temperature.
Hull Volume Chart
The following examples assume a block coefficient of 0.55. They show how hull volume changes as the principal dimensions increase.
| Length | Beam | Draft | Block Coefficient | Estimated Volume |
|---|---|---|---|---|
| 20 ft | 8 ft | 3 ft | 0.55 | 264 ft³ |
| 25 ft | 9 ft | 3.5 ft | 0.55 | 433.1 ft³ |
| 30 ft | 10 ft | 4 ft | 0.55 | 660 ft³ |
| 35 ft | 11 ft | 4.5 ft | 0.55 | 951.4 ft³ |
| 40 ft | 12 ft | 5 ft | 0.55 | 1,320 ft³ |
| 50 ft | 14 ft | 6 ft | 0.55 | 2,541 ft³ |
How do you calculate hull volume in cubic meters?
When the hull dimensions are already measured in meters, use:
$$V_{m^3} = L_m \times B_m \times T_m \times C_b$$
For example, a hull measuring 9.144 m long, 3.048 m wide, and 1.2192 m deep with a block coefficient of 0.55 has an estimated underwater volume of approximately 18.69 m³.
How do you calculate hull volume in cubic feet?
If the dimensions are in feet, the result is automatically in cubic feet:
$$V_{ft^3} = L_{ft} \times B_{ft} \times T_{ft} \times C_b$$
How do you convert cubic feet to cubic meters?
One cubic foot is approximately 0.0283168 cubic meters.
$$m^3 = ft^3 \times 0.0283168$$
Conversely:
$$ft^3 = m^3 \times 35.3147$$
How do you convert hull volume to liters?
One cubic meter contains 1,000 liters:
$$Liters = m^3 \times 1,000$$
Therefore, a hull volume of 18.69 m³ corresponds to approximately 18,690 liters.
How do you calculate the volume of a boat hull?
A preliminary hull-volume estimate can be made from the three principal dimensions and the block coefficient:
$$Hull\ Volume = Length \times Beam \times Draft \times C_b$$
For greater accuracy, naval architects normally use detailed hull geometry, offsets, sectional areas, or computer-aided hull models rather than only the principal dimensions.
Does hull volume change with draft?
Yes. As draft increases, more of the hull is submerged and the displaced volume generally increases.
The simple formula assumes a constant block coefficient, so it is best considered an estimate. The actual relationship between draft and displacement depends on the shape of the hull.
Does beam affect hull volume?
Yes. With length, draft, and block coefficient held constant, increasing beam increases the estimated hull volume proportionally.
$$Beam \times 2 \Rightarrow Hull\ Volume \times 2$$
In a real boat, changing the beam usually also changes the hull shape, so the block coefficient may change as well.
Does hull length affect volume?
Yes. If beam, draft, and block coefficient remain unchanged, doubling length doubles the estimated hull volume.
$$Length \times 2 \Rightarrow Hull\ Volume \times 2$$
What is the formula for block coefficient?
$$\boxed{ C_b = \frac{V} {L \times B \times T} }$$
If the actual displacement volume and the principal dimensions are known, the block coefficient can be calculated from this equation.
What is the formula for hull volume?
$$\boxed{ V = L \times B \times T \times C_b }$$
This is the principal equation used by this calculator.
Hull Volume FAQ
Hull volume can be estimated by multiplying length × beam × draft × block coefficient.
The block coefficient describes how full the underwater hull is compared with a rectangular block having the same length, beam, and draft.
You can calculate the surrounding rectangular volume using length × beam × draft, but this will generally overestimate the actual hull volume because a boat hull is not rectangular.
No. Hull volume is a volume measurement. Displacement is related to the mass or weight of water displaced by the submerged hull.
One cubic meter equals 1,000 liters.
One cubic meter is approximately 35.3147 cubic feet.
No. Hull volume calculated from length, beam, draft, and block coefficient represents the underwater hull volume. It does not represent usable cabin, storage, or interior volume.
Yes. Underwater volume can be multiplied by the density of the surrounding water to estimate displaced mass.