A few variables need to be considered when calculating the theoretical coverage of a spray nozzle. The spray angle plays a role and is usually measured near the orifice of the nozzle. This may vary depending on the type of nozzle you are using.
The second variable to consider is the spray distance. The spray distance will have an impact on the width of the spray coverage. It should also be noted that the greater the distance, the less accurate the coverage. This is due to the effects of gravity and various ambient conditions.
Another factor to consider is the viscosity of the liquid being sprayed. An increase of the viscosity can reduce the spray angle, therefore affecting the overall spay coverage.
The table below lists the theoretical coverage at various distances in relation with the spray angle: