It's 12" x 12" http://www.miamimaritimelaw.com/divinglaws.htm
QuoteDisplay MoreFLORIDA DIVING LAWS
327.331 Divers; definitions; divers-down flag required; obstruction to navigation of certain waters; penalty.--
(1) As used in this section: (a) "Diver" means any person who is wholly or partially submerged in the waters of the state and is equipped with a face mask and snorkel or underwater breathing apparatus.
(b) "Underwater breathing apparatus" means any apparatus, whether self-contained or connected to a distant source of air or other gas, whereby a person wholly or partially submerged in water is enabled to obtain or reuse air or any other gas or gases for breathing without returning to the surface of the water.
(c) "Divers-down flag" means a flag that meets the following specifications:
1. The flag must be square or rectangular. If rectangular, the length must not be less than the height, or more than 25 percent longer than the height. The flag must have a wire or other stiffener to hold it fully unfurled and extended in the absence of a wind or breeze.
2. The flag must be red with a white diagonal stripe that begins at the top staff-side of the flag and extends diagonally to the lower opposite corner. The width of the stripe must be 25 percent of the height of the flag.
3. The minimum size for any divers-down flag displayed on a buoy or float towed by the diver is 12 inches by 12 inches. The minimum size for any divers-down flag displayed from a vessel or structure is 20 inches by 24 inches.
4. Any divers-down flag displayed from a vessel must be displayed from the highest point of the vessel or such other location which provides that the visibility of the divers-down flag is not obstructed in any direction.
(2) All divers must prominently display a divers-down flag in the area in which the diving occurs, other than when diving in an area customarily used for swimming only.
(3) No diver or group of divers shall display one or more divers-down flags on a river, inlet, or navigation channel, except in case of emergency, in a manner which shall unreasonably constitute a navigational hazard.
(4) Divers shall make reasonable efforts to stay within 100 feet of the divers-down flag on rivers, inlets, and navigation channels. Any person operating a vessel on a river, inlet, or navigation channel must make a reasonable effort to maintain a distance of at least 100 feet from any divers-down flag.
(5) Divers must make reasonable efforts to stay within 300 feet of the divers-down flag on all waters other than rivers, inlets, and navigation channels. Any person operating a vessel on waters other than a river, inlet, or navigation channel must make a reasonable effort to maintain a distance of at least 300 feet from any divers-down flag.
(6) Any vessel other than a law enforcement or rescue vessel that approaches within 100 feet of a divers-down flag on a river, inlet, or navigation channel, or within 300 feet of a divers-down flag on waters other than a river, inlet, or navigation channel, must proceed no faster than is necessary to maintain headway and steerageway.
(7) The divers-down flag must be lowered once all divers are aboard or ashore. No person may operate any vessel displaying a divers-down flag unless the vessel has one or more divers in the water.
1(8) Any willful violation of this section shall be a misdemeanor of the second degree punishable as provided by s. 775.082 or s. 775.083.
(8) Except as provided in s. 327.33, any violation of this section shall be a noncriminal infraction punishable as provided in s. 327.73.
Note.--Former s. 861.065.
A legal size diver down flag is available from Speardiver. Comes in two sizes, for float 12.5" x 11", and for boat 24" x 20" Diver Down Flag - Speardiver I figured this will be important to some of you because of the improved stiffener system. I'm very tired of replacing flags when the grommets pull out of the flag material because of the conventional wire stiffener.
Features
- Flag has a stitched-in fiberglass stiffner. Superior to the conventional wire stiffner which gets entangled with other gear in your equipment bag, bends and requires constant straightening, and causes the grommets to rip out of the flag material rendering the flag illegal and unusable.
- High quality nylon construction.
- Stainless steel grommets.
- White stripe is stitched on. Will not fade and rub off like a painted on stripe.
- Boat size flag accepts the cheapest and most readily available flag pole; a 1/2" white PVC pipe