Throw ratio is the ratio of Throw Distance to the Screen Width. Throw Ratio =Throw Distance / Screen Width. The greater the throw Ratio, the farther the distance required for the same screen size.
Throw distance is the distance from the projector lens to the screen.
For example, your desired screen is 100”; if the throw ratio is 0.39:1, the throw distance is just 86.64 cm, but if the throw ratio is 1.2:1, a throw distance of 266.58 cm is required to get the same screen size.
Currently, the common throw ratio for the home projector is 1.2:1.