555 Timer Calculator
Calculate frequency, period, and duty cycle in astable mode, or pulse width in monostable mode. All resistance and capacitance units supported.
Enter all values to compute the result
Astable
Reference formulas
In astable mode the 555 oscillates continuously between its high and low thresholds. R1 and R2 charge the capacitor; R2 alone discharges it. The duty cycle is determined by the ratio (R1+R2)/(R1+2R2).
Frequency
f = 1.44(R1 + 2R2) · C1
Duty cycle
D = R1 + R2R1 + 2R2 × 100%
High time
TH = 0.693 · (R1 + R2) · C1
Low time
TL = 0.693 · R2 · C1
Legend
R₁ — charge resistorR₂ — charge/discharge resistorC₁ — timing capacitor