555 Timer — Astable Mode Calculator

Enter RA, RB (in ohms) and the capacitor value + unit. The page will compute period, frequency, T_high, T_low, and duty cycle.

RA (Ω) RB (Ω) Capacitor

Formulas used:

T = 0.693 × (RA + 2·RB) × C

T_high = 0.693 × (RA + RB) × C

T_low = 0.693 × RB × C

f = 1 / T

Results

Period (T)

—

Frequency (f)

—

T_high

—

T_low

—

Duty Cycle

—

Tip: use realistic resistor values (Ω) and capacitor units. Small rounding errors can happen with very large/small numbers.