Design Pressure (DP): how much wind it takes
The DP rating tells you how much wind pressure a window is built to handle, in pounds per square foot. Higher is stronger. In Florida, you'll commonly see DP 50 and up on impact products. The right DP for your home depends on your location, the building height, and where the window sits on the house — your installer should match the rating to the code requirements for your address, not just sell you the biggest number.
Performance Grade (PG): the whole package
PG is similar to DP but rates the complete window unit — frame, glass, and hardware together — under a newer testing standard. You'll see PG ratings on newer product lines. Like DP, higher means it handled more pressure in testing.
U-factor: how well it insulates
U-factor measures how easily heat passes through the window. Lower is better. Old single-pane windows have high U-factors (heat pours through); modern insulated impact units are much lower. In Florida's climate, U-factor matters, but it's not the headline number — see below.
SHGC: the Florida number that matters most
Solar Heat Gain Coefficient measures how much of the sun's heat gets through the glass. Lower is better in Florida — a low SHGC means less solar heat baking your rooms. If you remember one efficiency number for Orlando, make it this one. Good low-E coatings drive SHGC down while keeping the glass clear.
How to use ratings when comparing quotes
Ask every bidder for the DP/PG rating, U-factor, and SHGC of the exact product they're quoting — not the brand's best numbers, the numbers for your windows. Then compare like with like. A cheaper window with a much higher SHGC will cost you in cooling bills for decades. The label tells the truth; make sure you see it.