The short answer

Add up the weight of the dock and everything you expect on it, multiply by a safety factor, and choose floats whose combined buoyancy rating meets or beats that number. For most residential docks, a safety factor of about 2.0 is a sensible starting point.

This number decides how your dock feels underfoot. With too little float, the deck rides low and dips when a few people gather on one side. With too much, you've spent money on buoyancy you'll never use and your dock can sit too high out of the water.

Step 1: Add up your dead load and live load

Your total load has two parts: dead load, which never leaves the dock, and live load, which comes and goes.

Dead load is the frame, decking, floats and hardware, plus any share of a gangway that rests on the dock. Use these planning weights to get started:

Material	Planning weight (lb per sq ft of deck)
Wood frame	4.0
Aluminum frame	2.5
Composite decking	3.0
Pressure-treated decking	2.5
Titan Deck	1.6

Steel truss frames are built in sections, so use the weight of each section from its spec sheet. Add cleats, bumpers, ladders and lighting as a separate line.

Live load is the people and gear you expect at the busiest moment. Count about 200 lb per person, then add coolers, furniture and kayaks. A boat tied alongside floats itself and adds little, but a lift or rack mounted on the dock counts in full.

Be honest about that busiest moment. If you host ten people on the Fourth of July, design for ten, even if most days it's just you and a fishing rod.

Step 2: Apply a safety factor

Multiply your total load by a safety factor to get the buoyancy you need.

Required buoyancy = (dead load + live load) × safety factor

Dock type	Safety factor
Light use, minimum	1.5
Standard residential	2.0
Commercial or public	2.5 or more

A factor of 2.0 also tells you how the dock will ride. At your full design load, the floats sit about half underwater, with the other half in reserve.

That reserve covers the things you can't plan for, like a crowd bunching at one corner. It also covers normal variation in the floats themselves, since Permafloat lists its tank-tested ratings at +0/-5%. Overloading is also excluded from the float warranty, so it pays not to run the numbers tight.

Worked example: an 8' x 24' residential dock

This dock needs 7,568 lb of buoyancy, and six 36" x 72" x 16" floats cover it with 844 lb to spare.

Here's the load for a wood-framed dock with Titan Deck and 192 sq ft of deck:

Item	Weight (lb)
Wood frame (192 sq ft x 4.0)	768
Titan Deck (192 sq ft x 1.6)	307
Cleats, bumpers, ladder and other hardware (estimate)	125
Six floats (6 x 64 lb)	384
Dead load	1,584
Ten people at 200 lb, plus 200 lb of gear	2,200
Total load	3,784
Required buoyancy at a 2.0 safety factor	7,568

The floats count toward the dead load, so the requirement shifts slightly with each option. Here's how four Permafloat layouts compare:

Layout	Total buoyancy (lb)	Required (lb)	Margin (lb)	Result
6 x 36" x 72" x 16"	8,412	7,568	844	Our pick
4 x 48" x 96" x 16"	10,072	7,664	2,408	Most reserve, for heavier use
4 x 48" x 72" x 16"	7,520	7,456	64	Passes, but with almost no room to add anything
6 x 48" x 48" x 16"	7,452	7,484	-32	Falls just short

With six 36" x 72" x 16" floats, about 13" of each float stays above the water with only the dock's own weight on it. That drops to about 9" with all ten people and their gear aboard.

Check your local rules too. Headcount isn't the only way to set live load, and some codes specify pounds per square foot. For example, some states requirements call for 20 lb per sq ft for private floating docks and 30 for public ones, with at least 3" of float above the water under full load.

Our example passes the private figure with about 5.7" of float showing. At the public figure it leaves only about 2", so it would need more flotation. Always confirm what applies to your lake and county.

Step 3: Choose the footprint and depth

Footprint sets how much the dock moves under a load, and depth sets how much reserve you have and how high it rides.

Footprint controls stability. A wider, longer float spreads the load over more water, so the same weight sinks it less. To estimate this, divide a float's rating by its depth:

16" deep float	Buoyancy (lb)	Lb per inch of sink (approx.)
24" x 48"	598	37
36" x 72"	1,402	88
48" x 72"	1,880	118
48" x 96"	2,518	157

Depth controls reserve and height. Going deeper adds capacity without changing how much the dock dips per person. A 48" x 72" float gives about 115 to 118 lb per inch whether it's 12", 16", 20" or 24" deep, but its rating climbs from 1,420 lb to 2,786 lb.

The deeper float also rides higher, because more of it stays above the water. That matters if you need the deck to line up with a boat or gangway.

To estimate where the dock will sit, use this formula:

Inches underwater = (total load ÷ total buoyancy) × float depth

Subtract that from the float depth to get the float height above water, then add your frame height to get the deck height.

Step 4: Lay the floats out evenly

Spread the floats so each part of the dock carries its share, and keep them toward the outer edges, where they resist tipping best.

In this layout, the floats run 18 ft along each 24 ft side, with even gaps between them. If a gangway lands on one end, check whether that end needs added flotation.

Follow Permafloat's installation rules. These are required under the float warranty:

• Frame support: Support both the sides and ends of each float, with frame support at least every 48" x 48" (16 sq ft).
• Mounting slots: Use at least four slots on floats 4 ft long or shorter. On longer floats, use all the slots along the sides and at least one hole or slot in every corner.
• Tides and waves: Bolt or lag every mounting slot if the dock sees tidal changes or strong wave action.
• Fasteners: Use 3/8" or larger bolts or lag screws, in galvanized or stainless steel.
• Handling: Lift dock sections with floats attached instead of sliding them.

Add flotation where extra weight lands. A gangway hinged at the shore puts roughly half its weight and foot traffic on the dock, so that end needs more lift. Georgia's appendix, for example, designs gangway landing flotation for 50 lb per sq ft of live load. Anything heavy and fixed, like a lift or a dock box, also needs float beneath it.

Avoid these common mistakes:

• Leaving out weight: The floats, hardware and gangway all count.
• Judging by deck height: A tall frame can make a dock look high in the water, but only the float above the waterline adds reserve.
• Sizing for an average day: Design for your busiest day instead.

Dock Float FAQ

How much weight can one dock float hold?

The rating gives the float's maximum lift, not a load to plan around. A 36" x 72" x 16" Permafloat is rated at 1,402 lb, but at a 2.0 safety factor you'd plan on about half of that.

How high will my dock sit in the water?

Divide your total load by your total buoyancy, then multiply by the float depth. In our example, 3,784 lb on 8,412 lb of buoyancy puts about 7" of a 16" float underwater, leaving about 9" above.

Does salt water change the math?

Only slightly. Salt water is denser than fresh water, so floats get a little more lift. We'd treat that as extra margin rather than a reason to buy less float.

Can I add floats to an existing dock?

Yes. Permafloat floats attach to new or existing wood, steel and aluminum frames. Rerun the numbers with your current weight, and make sure the frame can support each new float on its sides and ends.

Do I need an engineer?

For a commercial or public dock, or for unusual loads like a boat lift, we recommend having a licensed marine engineer review the design. Your local building department or lake authority can tell you what permits and standards apply.

Ready to run your numbers?

Plug your dock into our flotation calculator to see your required buoyancy and compare float options.

Then shop Permafloat dock floats, along with the frames, decking and hardware to finish the build.

Want a second opinion before you order? Call us at 704-477-5470 or email info@shoreline-supply.com with your dock size and how you plan to use it.

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