How to Measure a Jon Boat
Learn how to measure a jon boat correctly, including overall length, beam, bottom width, side height, draft, transom width, and weight. These measurements are useful when buying a cover, trailer, motor, accessories, replacement parts, or comparing boat sizes.
What measurements do you need for a jon boat?
For a basic size record, measure:
- Overall length
- Maximum beam
- Bottom width
- Side height
- Transom width
- Draft
- Transom height
- Boat weight
You may also need cockpit dimensions, deck dimensions, seat spacing, motor well dimensions, and interior measurements for specific accessories.
How do you measure the length of a jon boat?
Measure the boat from the foremost point of the hull to the rearmost point of the hull along the boat's centerline or the longest practical hull dimension.
Measure the actual hull rather than adding the length of an outboard motor, trailer, bow mount, or removable accessory.
Jon Boat Length: front of hull → rear of hull
For boats with unusual bows or transoms, check the manufacturer's convention before comparing your measurement with a published model size.
How do you measure jon boat beam?
Beam is the boat's maximum width. Measure across the widest part of the hull, typically from one outer side edge to the opposite outer side edge.
For trailer and cover selection, the outside beam is usually the most useful measurement. For interior accessories, you may also need the inside width.
Maximum Beam: widest outside hull width
How do you measure the bottom width of a jon boat?
Bottom width is especially important on jon boats because it helps describe the shape and stability characteristics of the hull.
Measure straight across the flat or nearly flat bottom from one bottom edge to the other at the section where the bottom is widest, according to the measurement convention being used.
Do not assume bottom width is the same as beam. A jon boat can have a much wider overall beam than its flat bottom.
| Measurement | What It Describes |
|---|---|
| Beam | Maximum overall hull width. |
| Bottom width | Width across the hull bottom. |
| Inside width | Usable interior width between the sides. |
How do you measure jon boat side height?
Side height is the vertical distance from the bottom of the hull to the upper edge of the side at the measurement location.
Because a jon boat's sides may not be perfectly vertical and the height can vary along the hull, note where the measurement was taken.
Side height is sometimes described as depth in boat specifications, but the exact terminology can vary between manufacturers.
How do you measure jon boat draft?
Draft is the vertical distance between the waterline and the lowest submerged part of the hull or appendage under a defined loading condition.
For a jon boat, measure draft while the boat is floating normally in calm water and loaded in the condition you want to document.
$$Draft = Waterline\ to\ Lowest\ Submerged\ Point$$
Outboard engines, lower units, transducers, and other equipment can extend below the hull, so specify whether you are measuring bare hull draft or the lowest operating component.
How do you measure a jon boat transom?
Measure the transom width across the area where the motor and mounting hardware are attached. Also record the transom height because it affects the appropriate outboard shaft length.
If you are buying an outboard, the transom height measurement is usually more important than simply knowing the boat's overall length.
How do you measure jon boat transom height?
Measure vertically from the top of the transom mounting surface to the bottom of the hull at the centerline of the transom.
This measurement is commonly used when determining whether an outboard with a short, long, or extra-long shaft is appropriate.
Transom Height: top of motor-mounting surface → bottom of hull
How do you measure a jon boat for a cover?
A boat cover generally requires more than just the hull length. Measure the overall hull length, maximum beam, windshield or console height if present, and the location of consoles, seats, rails, trolling motors, and other structures.
If the cover manufacturer provides a size chart, compare your actual dimensions with the chart instead of selecting a cover from length alone.
How do you measure a jon boat for a trailer?
Trailer selection can require overall hull length, transom width, hull bottom shape, weight, center of gravity, and the distance from the transom to the appropriate support points.
The trailer must also be rated for the combined weight of the boat, motor, fuel, batteries, equipment, and other carried load.
$$Trailer\ Load = Boat + Motor + Fuel + Batteries + Gear$$
How do you measure a jon boat for an outboard motor?
Start with the transom height. This determines the general shaft-length category required by the engine. Also check the maximum horsepower rating and maximum engine weight specified for the particular boat.
Do not choose an engine from boat length alone. The boat's capacity plate or manufacturer documentation should be used for the permitted horsepower and engine size.
How do you measure a jon boat's weight?
The most reliable method is to use the manufacturer's published weight for the exact model and configuration. If you are weighing the boat yourself, make sure you define what is included.
A boat's actual transport weight can include the hull, motor, batteries, fuel, accessories, and equipment.
Why is bottom width important on a jon boat?
Bottom width provides useful information about the shape of the flat bottom and the amount of hull surface supporting the boat at the waterline. It is also commonly used when comparing different jon boat designs.
Bottom width alone does not determine stability, carrying capacity, or performance. Those characteristics also depend on hull shape, beam, weight distribution, draft, freeboard, and loading.
What is the difference between beam and bottom width on a jon boat?
Beam is the maximum overall width of the hull. Bottom width is the width of the hull's bottom surface. A flat-bottom jon boat usually has a bottom width that is smaller than its maximum beam.
How do you measure the inside of a jon boat?
Measure from inside sidewall to inside sidewall at the location where the dimension is needed. For a fishing deck, seat, cooler, or storage accessory, also measure the length available between benches, consoles, ribs, and other obstructions.
How do you measure a jon boat for a floor or deck?
- Measure the inside length of the area to be decked.
- Measure the inside width at several locations.
- Record changes around benches, ribs, and sidewalls.
- Measure the height available for the new floor system.
- Create a cardboard template for irregular sections.
- Account for the thickness of the flooring material.
Measuring in several places is important because jon boat hulls can taper toward the bow and stern.
What tools do you need to measure a jon boat?
A tape measure is enough for most basic dimensions. A straightedge, ruler, caliper, level, plumb line, and measuring stick can help with more precise measurements.
For irregular interior areas, cardboard or paper templates can be more useful than trying to record dozens of individual measurements.
What are the most common jon boat measuring mistakes?
- Confusing beam with bottom width.
- Measuring interior width when an outside dimension is required.
- Including the outboard or trailer in hull length.
- Forgetting to measure transom height.
- Using dry weight when transport weight is required.
- Taking only one width measurement on a tapered hull.
- Ignoring seats, ribs, consoles, or other obstructions.
- Mixing inches, feet, millimeters, and centimeters.
How to measure a jon boat step by step
- Measure overall hull length.
- Measure maximum outside beam.
- Measure the flat bottom width.
- Measure side height or hull depth.
- Measure transom width.
- Measure transom height.
- Measure draft if the boat is in the water.
- Record the boat's actual weight or manufacturer's published weight.
- Record important interior dimensions for the accessory you are fitting.
Jon boat measurement FAQ
It depends on the purpose. Overall length and beam are useful for general sizing, while bottom width and transom height can be more important when comparing hulls or selecting an outboard.
Usually the model name refers to an approximate nominal hull length. Your actual measurement may differ slightly depending on the manufacturer's measurement convention.
Measure the maximum outside width of the hull, then compare it with the cover manufacturer's size chart and account for consoles, rails, motors, and other structures.
Measure the transom height, then check the boat's maximum horsepower and engine-weight ratings before selecting an engine.
No. Beam is the maximum overall hull width. Bottom width is the width of the bottom surface and is normally smaller on a jon boat.
Measure hull length, transom width, hull shape, and weight, then match those dimensions to the trailer's support layout and capacity.