PWM arduino uno problem?

zacmackra:
Hey guys i have been studying pwm in arduino uno. The o/p in arduino uno is from y= 0 to 255 which can be used as pwm like this analogWrite(x,y);

What i want to know is, is there any unit for this number 0-255? It must be related to duty cycle. Can anybody tell me how to calculate duty cycle?

No unit.

0 is completely off. 255 is completely on. 128 is about 50%. on, 50% off.