To calculate your glide distance, you need to know the glide ratio at best glide of your aircraft. Here is an example from a Cessna 152:
Which shows that for every 1000 feet of altitude AGL a Cessna 152 should be able to glide 1.6 nautical miles. 1.6 nautical miles is 9722 feet, so this corresponds to a glide ratio of about 9.7 to 1. But since we usually think of altitudes in feet and ground distances in nautical miles, the figure 1.6 nautical miles per 1000 feet is probably more useful.
If your glide ratio is 1.5 nautical miles per 1000 feet, your math is correct. But that is just a common rule of thumb and may not be the correct ratio for your aircraft.
I don't know where you got 9:5. At a guess it is supposed to be 9:1 (which corresponds to around 1.5 nautical miles per 1000 feet).
Keep in mind that these are not calculations you will be relying on much in the cockpit. In a real engine-out situation there will be winds which will extend your glide (for a tailwind) or shorten it (for a headwind). The true best glide airspeed also depends on the wind speed- with a headwind you will want to be on a slightly faster airspeed and slightly slower for a tailwind.
In the cockpit, visual references will tell you how far you can glide- a spot that appears to be moving down in the windscreen is one that you will glide over at your current glide ratio, while one that is moving up in the windscreen is one that you will land short of. The spot you are gliding to is the spot that doesn't move.