Tools / 555 Timer Calculator ⏲️ 555 Timer Calculator Compute frequency, period, and duty cycle for 555 astable and monostable circuits. Mode Astable (oscillator) Monostable (one-shot) Ra (Ω) Rb (Ω) C (F) Supports n, u, p suffixes. R (Ω) C (F) Supports n, u, p suffixes. Calculate Reset Results