Use this 555 Timer calculator to find the output based on you resistor and capacitor values.
You can choose between astable mode and monostable mode. The astable mode will give you a frequency calculator plus time high/low. The monostable calculator will give you the output pulse duration.
Check out the complete 555 Timer tutorial to learn more.
Choose Configuration
R1 Resistor Value
R2 Resistor Value
C1 Capacitance Value
Formula
Th = 0.693(R1 + R2)C1
Tl = 0.693R2C1
f =
1.44
(R1 + 2R2)C1
Time High
Time Low
Frequency