Boat Capacity

The maximum number of people that can be on a boat at a given time and the total weight a boat can safely handle are both critically important to know. All vessels twenty feet in length or less are required to post this information on a capacity plate. Exceeding these maximums is a safety concern, and abiding by them is the law.

Capacity plates are fastened near the steering area or the helm and display the maximum number of adults, the maximum gross load, and the maximum engine size, in horsepower, that a boat can legally carry.

The maximum gross load listed on the capacity plate is the total weight your boat can handle. This weight includes people, equipment, stores, fuel, engine assembly, and steering controls. If a boat doesn’t have a capacity plate, the boat capacity can be calculated using the following formula.

Boat Capacity Calculator

The number of people you can take on board safely can be found by using the following equation.

Number of people = vessel length (ft.) x vessel width (ft.) ÷ 15

First, find the length and width of your boat in feet, then use this calculator to find out your boat’s capacity.

PWCs do not have capacity plates. Always follow the recommended capacity in the owner’s manual and on the manufacturer’s warning decal.

The capacity plate also lists the maximum engine power for your boat, indicated in horsepower. The maximum engine power applies only to boats powered by outboard engines, and it must never be exceeded.

Maximum Person Capacity

When determining the maximum person capacity, boat manufactures consider a number of variables. The first being the weight of each person.

The average weight used by boat manufacturers to calculate maximum capacity is about one hundred and fifty pounds per person. If the passengers on a boat have weights above that threshold, or if the weight of supplies is too great, the number of passengers should be adjusted.

Maximum Horsepower

If you’re operating a small flat-bottomed boat and don’t have a capacity plate, you can easily calculate the engine size that is safe for your vessel by using the following formula.

Maximum horsepower can be calculated using the following formula. 

Boat length x boat width = boat square footage

The square footage of the boat is found by multiplying its length by the width of the transom.

Once the square footage is found, use the calculator below to find your boat’s maximum horsepower. A twelve-foot boat with a transom width of four feet translates to a boat with 48 square feet, which can be operated safely with an engine that has up to 15 horsepower.

Boat Maximum Horsepower Calculator

Length x WidthMaximum Horsepower
35 feet or less3
36 - 39 feet5.5
40 - 42 feet7.5
43 - 45 feet10
46 - 52 feet15

Overloading or Overpowering

Overloading or overpowering your boat is extremely dangerous. An overpowered boat is hard to control. An oversized engine will cause your boat to sit too low in the stern, which will make it susceptible to being swamped by its own wake or that of another boat.

Overloading a boat with people or supplies can also lead to swamping. Even if the boat is within its maximum allowable weight, the load must be distributed evenly, with the weight focused on the center of the boat. This will help to stabilize the boat and prevent capsizing or swamping.

Extra caution should be taken in inclement weather. A heavy boat is harder to control, especially when there are higher waves.

Carrying a lighter load is always the safest way to navigate rough waters

You should also read:

Boating Terminology

Parts of a Boat