Boating Basics Online is reader-supported. When you buy via our links, we may earn a commission at no cost to you. Learn more

How Are Boats Measured? (Length, Width & Height)

Written by J. Harvey / Fact checked by S. Numbers

how are boats measured

The length of a boat will always be one of its most important aspects because it overlaps numerous essential factors every time you take it out to sea.

As far as the question “How are boats measured?” is concerned, we don’t depart from the fundamentals like knowing its exact length, width, and height.

The significance of knowing the exact boat length measurement is proven by the need to know the vessel’s length overall, length on deck, and waterline length, to cite a few. These are often tallied in order to adhere to regulations and other important considerations.

Read on to find more about the correct way to measure a boat.

The Different Ways Boats Are Measured


To know how to measure a boat thoroughly, we have to look at both the units that need to be measured and the ways to calculate and quantify them. These are the main parameters you have to look at:

  • Length – This unit often takes the spotlight because it includes critical elements such as length overall, length on deck, and waterline length. It’s also what helps to determine boat classifications.
  • Width – To measure the width of a boat is to know its beam, which is its upper surface’s widest extent. The average width of a boat is 8 fee
  • Height – This is concerned with the distance between the beam’s highest point up to the bottom-most portion of the hull. It could also refer to the freeboard or the distance between the deck and the waterline.

Height (what builders refer to when they measure the depth of a boat) also determines draft (the distance between the waterline and the bottom of the vessel). To elaborate, the taller the boat, the more draft it’ll require to run smoothly.

Length is the more prominent of the three, though. After all, an operator measure the length of their vessel to get vital measurements such as the following:

  • Length Overall (LOA) – Most state laws require knowledge of this exact parameter not only to identify the vessel’s true size but also the amount of boating and safety equipment it needs to have onboard. It also influences the vessel’s performance and speed, among others.
  • Length on Deck – This is often confused with the length overall (LOA). However, usually, this only accounts for the (you guessed it!) deck’s length and leaves out the protrusions.

It can also be used to approximate boat dimensions and, thus, its total size, though.

  • Waterline Length (LWL) – This refers to the vessel’s length with regard to its current waterline. As such, it accounts for the submerged portion of the hull only, so LWL will typically be shorter than LOA.

How to Measure the Length of a Boat


Most shipwrights and boat owners will measure the length of a boat using something as simple as a tape measure. Of course, you’ll need to be specific about the exact length parameter you’re trying to pinpoint.

Are you trying to measure the overall length or the waterline length? Follow these guidelines to learn how are boat length measured:

1. Overall Length

Normally, the LOA includes all the protrusions. You can start from the bow’s tip and end at the stern’s furthest point. Keep the tape straight and taut while taking the measurement!

At best, how we measure it readily reveals the exact length overall definition. Basically, it’s the vessel’s “true length,” as it includes everything attached to it.

2. Length on Deck

Measure only the length of the deck minus protrusions.

3. Waterline Length

Measure from bow to stern as well, but keep only the submerged portion of the hull in mind. You can usually rely on the grime build-up from the dirty water to measure the waterline length.

However, if there is no impurity mark on the boat, you’ll have to use a pen to mark every 1 foot or so on the vessel when it’s docked. Once it’s back on land, you can use a tape measure to size it.

Incidentally, do you know what unit would be best for measuring a boat’s length? Well, if you look at standard boat listings, they often tell the vessel’s size outright using feet.

It’s really a matter of feet being a simpler unit of measurement than most, plus the fact that it has been an ongoing tradition set by the British.

Why Are the Measurements of a Boat Important?


Overall, length plays more of a central role because of the following facts:

  • There’s no better way to be familiar with average boat size and the exact size of your own vessel than taking these measurements. You’ll be able to figure out its legal size and know the exact safety and operation regulations you need to be mindful of before going out to sea or lake.
  • You’ll have a good idea of its exact capacity in terms of payload, passengers, and cargo.
  • You’ll be able to know its strengths and weaknesses performance-wise more intimately. Waterline measurements have been the standard gauge for determining racing performance, for example.
  • You’ll be able to know the exact storage requirements for your boat.
  • Overall, in order to operate and sell it legally, you need to know a vessel’s exact dimensions.
  • Insurance companies need to determine how large or small your vessel is to know its exact premium.
  • You need to know how many crew you need to bring along at the minimum.
  • Taking the exact boat height measurement as well as length and width allows builders and owners to make the necessary improvements. For example, did you know that small fishing boats in Japan have had their hulls measured to make them more efficient?
  • How will you be able to know the exact cover for your boat if you don’t know how long it is? Boat covers need to be a snug fit, but not overly so, to avoid potential problems.


What about swim platforms?

If you’re trying to measure the exact length overall of your vessel, you need to include accessories like swim platforms in your boat measurements.

However, if you’re only trying to find out something specific such as length on deck or taking waterline measurements, you can leave them out.

What device is used to measure a boat?

As I’ve said above, feel free to use a tape measure you have on hand. You can also use telemeters, assuming you’ve got them, to measure a boat length.

Most owners who measure both their boat and its trailer rely on a tape measure, protractors, and a trailer measurement form for noting down the dimensions, usually handed out by the trailer manufacturer.


I hope that by finding out exactly how are boats measured, you’ve come to the same conclusion that it’s a fairly straightforward process. The facts above also outline and underline the reasons why people measure these vessels.

Thankfully, it’s not as complicated as, say, measuring boat chemistry. All I’m going to say is that you shouldn’t overlook these dimensions, especially if you want to get the most out of your boat, not only when you’re operating it but presenting it to potential buyers.

Read more: Tips to measure a boat steering cable.

5/5 - (2 votes)