In short
- Common guides size a cleat at 1 in of length per 1/16 in of line diameter: a 1/2 in line needs an 8 in cleat.
- Line size comes from the boat: about 1/8 in per 9 ft for everyday lines, and BoatUS sizes hurricane lines larger.
- Cleats fail at the bolts and the wood as often as at the cleat, so ask for through-bolts and backing plates.
- Cleat counts are our planning assumption: no source publishes one.
On this page
This dock cleat size calculator is for Cape Coral boat owners who tie up at a canal dock. Enter your boat length and it returns the line size, the cleat length that matches it for everyday docking and for hurricane lines, and how many cleats to ask a dock builder about. It uses published rules of thumb only, with no prices or brands. It pairs with the hurricane dock line calculator, which sizes the storm lines those cleats must hold.
En español: calculadora de tamaño y cantidad de cornamusas para un muelle de Cape Coral
Example: a 36 ft boat, with no existing cleat entered.
How the numbers are worked out
- Size the everyday line
Divide boat length by 9 and multiply by 1/8 in, never below 3/8 in, then round up to the next common size (3/8, 1/2, 5/8, 3/4, 7/8, 1 in).
- Match the cleat
Take 1 in of cleat length per 1/16 in of line diameter, tip to tip. A 1/2 in line gives an 8 in cleat.
- Add the storm line
Use the BoatUS hurricane line size for the boat length (1/2 in to 25 ft, 5/8 in to 34 ft, 3/4 to 1 in above) and match a cleat to it the same way.
- Count the cleats
Everyday docking needs 4 (bow, stern, two springs). Storm lines: our count is 6, 8 or 10 lines by boat size, so 2 lines to a cleat gives the low end and 1 line per cleat the high end.
Cleat length by boat length
| Boat length | Everyday | Storm |
|---|---|---|
| 20 ft | 6 | 8 |
| 28 ft | 8 | 10 |
| 36 ft | 8 | 12 |
| 56 ft | 14 | 12 |
Cleat tip to tip, in inches. The everyday cleat follows the 1/8 in per 9 ft line rule; the storm cleat follows the BoatUS hurricane line size. On larger boats the everyday rule can give the bigger cleat, because the two rules were written for different jobs. Cleats come in set sizes, so buy the next size up.
What the rules do not cover
A cleat is only as strong as what it is bolted to. In BoatUS Foundation cleat tests, fasteners failed first in most straight pulls, so bolt size and backing matter as much as cleat length. A cleat on a worn cap, a rotted post or a deck screwed to old pilings holds less than its size suggests. Ask the dock builder how each cleat is fastened and what it is fastened to, and see the hurricane dock line calculator for line length and chafe guards.
Pilings carry the load too: the dock piling calculator estimates how many a dock needs.
Cleat checklist
- Through-bolt. Stainless bolts, washers and nuts with a backing plate or solid blocking under the plank, not wood screws.
- Use the whole cleat. A line sized for a 10 in cleat on a 6 in cleat will crowd the horns and slip.
- Place them where lines run. Cleats near the bow and stern positions, with springs amidships, keep lines from crossing pilings.
- Round the edges. Rough cast edges chew line; smooth stainless or galvanized finishes last.
- Check before the season. Look for loose bolts, cracks and rust at the base before hurricane season.
Questions to ask a dock builder
- How will each cleat be fastened? Ask for through-bolts and backing plates, and what the cleat bolts into.
- Can existing cleats take storm loads? Ask them to check the cap, posts and bolts, not just the cleat.
- Do I need a permit to change the dock? See the dock and boat lift permit checklist.
- How do I choose a contractor? See choosing a seawall contractor.
Next step
This is a planning estimate, not an engineering design. We are a referral service, not a contractor; we connect visitors with independent local providers. Use the form below to ask independent marine and seawall contractors to check or add dock cleats.
Sources
- Waterfront Central, Dock Cleats 101: 1 in of cleat per 1/16 in of line diameter, tip to tip; 1/8 in of line per 9 ft of boat.
- EZ Dock, Dock Cleat Guide: a manufacturer chart of 6, 8, 10 and 12 in cleats by boat length, and a length x 0.2 formula (used here only as cross-checks).
- West Marine, How to Choose the Right Dock Lines: the 1/8 in per 9 ft rule and sizing up for surge.
- BoatUS Hurricane Preparation Guide: storm line sizes by boat length and the warning that cleats need real backing.
- BoatUS Foundation, Cleat Tests: cleats bolted to a steel plate and pulled to failure (circa 1990); fastener failure predominated in straight pulls.
Frequently asked questions
What size dock cleat do I need?
A common rule is 1 inch of cleat length (tip to tip) for every 1/16 inch of dock line diameter, so a 1/2 inch line calls for an 8 inch cleat. Treat that as a minimum, and go bigger if you double up lines or expect storm surge.
What size dock line goes with my boat?
A common rule of thumb is 1/8 inch of line diameter for every 9 feet of boat length, with 3/8 inch as the smallest practical size. A 36 ft boat works out to 1/2 inch line. For hurricane lines BoatUS lists larger sizes: 1/2 inch up to 25 ft, 5/8 inch to 34 ft and 3/4 to 1 inch above that.
How many dock cleats do I need?
For everyday docking, four lines (bow, stern and two springs) need four places to tie, so plan at least four cleats on the dock side. No source publishes a cleat count, so every count on this page is our planning assumption. For a hurricane the boat is held by 6 to 10 lines, tied to cleats and pilings.
Are bigger cleats always better?
Not by themselves. In BoatUS Foundation cleat tests, bolts and mounting failed more often than the cleat body in straight pulls. A big cleat on thin wood or small screws is only as strong as its fastening, so ask for through-bolts and backing plates.
Can I use the cleats I already have in a hurricane?
Maybe. Enter the length of your cleat above and the tool compares it with the everyday and storm sizes. Even a long enough cleat needs to be through-bolted into solid, sound structure, which an installer or marine surveyor can judge.