555 Timer Calculator
A 555 astable with 1 kΩ, 10 kΩ and 10 µF oscillates at 6.86998 Hz with a 52.4 % duty cycle.
6.86997638518554 Hz
Full answer, then cut to fewer decimals (not rounded):
- 6.86997638518554 Hz
- 6.8699763851855 Hz
- 6.869976385185 Hz
- 6.86997638518 Hz
- 6.8699763851 Hz
- 6.869976385 Hz
- 6.86997638 Hz
- 6.8699763 Hz
- 6.869976 Hz
- 6.86997 Hz
- 6.8699 Hz
- 6.869 Hz
- 6.86 Hz
- 6.8 Hz
- High time t_H = 0.693 (R₁ + R₂) C
- 76.24618986 ms
- Low time t_L = 0.693 R₂ C
- 69.31471806 ms
- Period
- 145.5609079 ms
- Duty cycle t_H/T
- 52.38095238 %
Step-by-step solution
- f = 1 ÷ (ln 2 × (R₁ + 2R₂) C) ≈ 1.44 ÷ ((R₁ + 2R₂) C)
- f = 1 ÷ (0.6931 × 21000 × 0.00001) = 6.869976385 Hz
- Duty = (R₁ + R₂) ÷ (R₁ + 2R₂) = 52.38095238 %
555 Timer Formula
f = 1/(ln 2 (R₁ + 2R₂)C) ≈ 1.44/((R₁ + 2R₂)C)
duty = (R₁ + R₂)/(R₁ + 2R₂); monostable T = ln 3 × RC ≈ 1.1RC
Worked Example
An astable 555 with R₁ = 1 kΩ, R₂ = 10 kΩ and C = 10 µF:
- f = 1 ÷ (ln 2 × (R₁ + 2R₂) C) ≈ 1.44 ÷ ((R₁ + 2R₂) C)
- f = 1 ÷ (0.6931 × 21000 × 0.00001) = 6.869976385 Hz
- Duty = (R₁ + R₂) ÷ (R₁ + 2R₂) = 52.38095238 %
Low time t_L = 0.693 R₂ C: 69.31471806 ms · Period: 145.5609079 ms · Duty cycle t_H/T: 52.38095238 %
GATE tip
The 555 thresholds sit at one and two thirds of Vcc, so its timing does not depend on the supply voltage, a point often asked in multivibrator questions.
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Frequently asked questions
Where do 0.693 and 1.1 come from?
The capacitor swings between Vcc/3 and 2Vcc/3: charging or discharging over that range takes RC ln 2 = 0.693RC. A monostable charges from 0 to 2Vcc/3, which takes RC ln 3 = 1.0986RC.
Can the duty cycle go below 50 %?
Not in the basic circuit, since t_H > t_L always. Add a diode across R₂ so the capacitor charges through R₁ only.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
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APA
Scientific Converters. (2026, October 15). 555 Timer Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/555-timer-calculator/
IEEE
Scientific Converters, "555 Timer Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/555-timer-calculator/