To calculate the injector size for a particular application:
Injector Flow Rate (lb/hr) =  Engine HP(1) x BSFC(2) Number of Injectors x Injector duty cycle(3) 
Or
Injector Flow Rate (cc/min) =  Engine HP(1) x BSFC(2) x 10.5 Number of Injectors x Injector duty cycle(3) 
This worksheet can do the calculations for you:
To calculate the horsepower capacity of injectors based on their flow rating:
Fuel injectors max HP (lb/hr)* = 
Injector flow rate x Number of injectors x 0.8
BSFC 
Or
Fuel injectors max HP (cc/min)* = 
Injector flow rate x Number of injectors x 0.8
BSFC x 10.5 
This worksheet can do the calculations for you:
Injector flow rate conversions:
Fuel injectors flow (lb/hr)* = 
Fuel injector flow (cc/min)
10.5 
Fuel injector flow (cc/min)* = 
Fuel injectors flow (lb/hr) x 10.5

This worksheet can do the calculations for you:
Injector flow rate conversions:




*NOTE: This formula take into account a properly functioning fuel delivery system. Damaged components, clogged or modified injectors, insufficient fuel delivery, or other fuel system problems that alter the injector flow rates will render this formula useless! 
Fuel Injector Flow Calculator