555 Timer Calculator
Calculate ideal monostable pulse time or astable timing from resistance and capacitance.
Ideal conventional 555 topology only. R in kΩ, C in nF, each 0.000001–1000000000. No device tolerances, leakage, supply limits, loading or operating-frequency validation. R2 is unused in monostable mode.
t = 1.1 RC; tH = ln(2)(R1+R2)C; tL = ln(2)R2C; f = 1/(tH+tL); D = tH/(tH+tL)
Result
A QUICK WALKTHROUGH
How to use this tool
- Choose the mode and enter the values.
- Read the formula and limitations before interpreting the result.
Formula and limits
Ideal conventional 555 topology only. R in kΩ, C in nF, each 0.000001–1000000000. No device tolerances, leakage, supply limits, loading or operating-frequency validation. R2 is unused in monostable mode. t = 1.1 RC; tH = ln(2)(R1+R2)C; tL = ln(2)R2C; f = 1/(tH+tL); D = tH/(tH+tL)
GOOD TO KNOW
Common questions
Does this evaluate a real component or circuit?
No. This is a nominal calculation from the inputs, not component selection or a safety assessment.