This NE555 timer calculator finds the output frequency and duty cycle of a 555 astable oscillator from your resistor and capacitor values. Enter R1, R2, and C above for instant results.
Formulas (astable mode)
Frequency f = 1.44 ÷ ((R1 + 2×R2) × C) Duty cycle = (R1 + R2) ÷ (R1 + 2×R2)
Example
R1 = 1 kΩ, R2 = 10 kΩ, C = 10 µF: f = 1.44 ÷ ((1000 + 20000) × 10µF) = 6.86 Hz, duty 52.4%.
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Frequently Asked Questions
How do I calculate 555 timer frequency?
Use f = 1.44 divided by (R1 plus 2 times R2) times C. Larger resistors or capacitor give a lower frequency.
What is the duty cycle of a 555 astable?
It is (R1 + R2) divided by (R1 + 2R2), always above 50% in the basic astable circuit.
Can a 555 reach exactly 50% duty?
Not in the basic circuit, but adding a diode across R2 lets the duty cycle approach 50%.