For the most common configuration (single inverter, feedback resistor + capacitor to input):
f ≈ 1 / (2.2 × R × C)
Example:
✅ This is close to simulation – but real frequency depends on: 74hc14 oscillator calculator
A good calculator will show you the min/max frequency range based on these tolerances.
If you want a 1 kHz signal:
Because the threshold voltages can vary slightly between manufacturers and temperature, most online calculators and engineers use a simplified approximation that works well for typical $5\textV$ operation:
$$ f \approx \frac0.8R \cdot C $$
(Note: Some datasheets, like NXP or Texas Instruments, might specify a constant closer to $0.7$ or $1.0$ depending on their specific internal hysteresis values. Always check the specific datasheet for critical timing applications.)