Signal Rise Time Calculator
Calculate signal rise time from system bandwidth or an RC network. Switch between modes to find rise time, the RC time constant, and the minimum oscilloscope bandwidth needed to accurately capture your signal.
For educational and reference use only. Always verify results before use in real-world designs or safety-critical applications. For more information, see Calculation Assumptions and Disclaimer.
How to Use This Calculator
Select a calculation mode using the toggle at the top of the calculator:
Bandwidth → Rise Time: Enter a system bandwidth and choose the appropriate unit (Hz, kHz, MHz, or GHz). The calculator will instantly show the corresponding 10–90% rise time and the minimum oscilloscope bandwidth required to measure it accurately.
RC Network → Rise Time: Enter a resistance and capacitance with their units. The calculator outputs the rise time, the RC time constant (τ), and the recommended oscilloscope bandwidth. A warning appears if the RC time constant is very large, indicating the circuit may significantly limit signal speed.
Formula
Bandwidth-limited rise time (single-pole system)
Where BW is bandwidth in Hz and tr is rise time in seconds (10%–90% transition time).
RC network rise time
Where R is resistance in ohms and C is capacitance in farads. Derived from the RC charging curve between 10% and 90% of the final voltage.
RC time constant
The time for the capacitor to charge to approximately 63.2% of the supply voltage. Rise time equals 2.2τ.
Minimum oscilloscope bandwidth
Use an oscilloscope with at least this bandwidth to measure rise time with reasonable accuracy. A 3–5× margin is recommended in practice.
Example
Bandwidth mode example
Given: BW = 100 MHz = 100,000,000 Hz
tr = 0.35 / 100,000,000 = 3.5 × 10⁻⁹ s
Rise time = 3.5 ns
RC mode example
Given: R = 1 kΩ = 1000 Ω, C = 100 pF = 100 × 10⁻¹² F
τ = R × C = 1000 × 100 × 10⁻¹² = 100 ns
tr = 2.2 × τ = 2.2 × 100 ns
Rise time = 220 ns
Frequently Asked Questions
What is signal rise time?
Signal rise time is the time a signal takes to transition from 10% to 90% of its final amplitude. It is a key measure of how quickly a circuit or signal responds to a change, and it directly relates to the system's bandwidth.
What is the formula for rise time from bandwidth?
For a single-pole system, rise time (tr) is related to bandwidth (BW) by the formula: tr = 0.35 / BW. This assumes a Gaussian or single-pole low-pass response.
How does an RC network affect rise time?
An RC network limits signal rise time due to the time the capacitor takes to charge through the resistor. The rise time for an RC network is approximately tr = 2.2 × R × C, where R is resistance in ohms and C is capacitance in farads.
What oscilloscope bandwidth do I need to measure a fast signal?
To accurately measure a signal's rise time, your oscilloscope's bandwidth should be at least BW = 0.35 / tr. As a practical rule, use an oscilloscope with at least 3–5× the bandwidth of your signal to avoid significant measurement error.
What is the RC time constant?
The RC time constant (τ) is the product of resistance and capacitance: τ = R × C. It represents the time for the capacitor to charge to approximately 63.2% of its final voltage. The rise time (10%–90%) equals approximately 2.2τ.