Enter the length, width, and weight of a boat into the calculator to estimate the draft of a boat. To make the calculation more accurate, add in the weights of individuals traveling on the boat to the overall weight.

Boat Draft Formula

The following formula is used to calculate a boat draft: 

DR = (W/D) / ( L*W) * 3
  • Where DR is the estimated draft (ft)
  • W is the weight of the boat (lbs)
  • L is the length of the boat (ft)
  • W is the width of the boat (ft)
  • D is the density of the water (lbs/ft^3)

To calculate a boat draft, divide the weight by the density, then divide this result by the result of the length divided by the width, then finally, multiply by 3.

This draft also does not include motors of rutters. Those should be added to the total draft.

What is boat draft?

Boat draft is a measure of the distance from the waterline to the bottom of the hull. It is used to estimate where a boat can travel safely based on water depth.

Boat draft is dependent on the overall shape of the boat, the weight of the boat, and the density of the water (i.e salt water or fresh water).

Example Problem

How to calculate boat draft?

The following example outlines the information and steps required to calculate the draft of a boat.

First, determine the length of the boat. Measuring the boat for this example yields a length of 35 feet.

Next, determine the width of the boat. For this example, the width is measured to be 10 feet.

Next, determine the weight of the boat. This boat comes out to a total weight of 13,600 lbs.

Next, determine whether the boat is in fresh or saltwater. This boat is in salt water, so the density is 64 pounds per cubic foot.

Finally, calculate the boat draft using the formula above:

DR = W/Density/(L*W) *3

DR = 13,600/64/35/10 *3

DR = 1.82 ft