Select average voltage slope, end voltage, start voltage or elapsed time, then enter the three displayed values. Voltages, times and slope units convert independently.
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Slew Rate Formula
The slew rate calculator determines how quickly an output voltage changes over a measured time interval. For most waveform measurements, the useful transition window is the span between the 10% and 90% voltage levels, because it captures the steep middle portion of the edge and is easier to measure consistently.
If you know the time at each threshold instead of the elapsed time directly, first compute the difference:
For a standard 10%-to-90% rise-time measurement of a step with amplitude Vstep, the voltage change across the interval is 80% of the full step:
| Term | Meaning | Common Units |
|---|---|---|
| SR | Slew rate, or rate of voltage change | V/s, V/ms, mV/ms, mV/s, V/µs |
| V90 | Output voltage at the 90% point of the transition | V, mV |
| V10 | Output voltage at the 10% point of the transition | V, mV |
| Δt | Elapsed time between the 10% and 90% points | s, ms, µs |
Rearranged Equations
Because the calculator can solve for a missing variable, these equivalent forms are also useful:
How to Use the Slew Rate Calculator
- Select the quantity to solve.
- Enter the three displayed known quantities and select their units.
- Choose the result unit and select Calculate.
If you are measuring from an oscilloscope, place one cursor at the 10% level and another at the 90% level, then use the time difference between those markers as the input for Δt.
Example Calculation
If an output rises from 2 V at the 10% point to 10 V at the 90% point in 10 µs, the change in voltage is 8 V. The slew rate is:
This means the signal is changing at 0.8 volts per microsecond over that measured interval.
What the Result Means
A larger measured slope magnitude means the voltage changed more quickly over this interval. A datasheet maximum slew rate is a separate large-signal specification. This is important in large-signal conditions where the output must move fast enough to follow a step, pulse, or high-frequency waveform without visibly rounding the edge.
- Higher slew rate: better ability to reproduce fast voltage transitions.
- Lower slew rate: greater chance of edge rounding, rate limiting, or large-signal distortion.
- Measured calculator result: the average slope across the interval you entered.
Required Slew Rate for Sine Waves
For sinusoidal signals, the minimum slew rate needed to reproduce the waveform without slew-induced distortion is:
If you know peak-to-peak voltage instead of peak voltage, use:
This relationship is useful when checking whether an amplifier can support a desired output amplitude at a given frequency.
Why 10% and 90% Are Used
The 10%-to-90% window avoids the flatter beginning and ending parts of a transition, where noise, settling, and trigger uncertainty can distort a measurement. Using the middle portion of the edge gives a more repeatable estimate of the meaningful voltage-change rate.
Practical Tips
- Select the unit of each voltage independently; the calculator converts them to a common basis.
- Enter the elapsed time between thresholds, not the total pulse width or signal period.
- Check decimal placement carefully when using microseconds or millivolts.
- For falling edges, enter the later voltage as End and earlier voltage as Start. The signed slope is negative; datasheet slew rate is often reported as a magnitude. Elapsed time must be positive, and its inverse requires a nonzero slope with a matching voltage-change sign.
- If your measured value seems unusually high, verify that you did not enter absolute timestamps instead of the time difference.
Applications
Slew rate calculations are commonly used when evaluating:
- Operational amplifiers
- Power amplifiers
- Signal conditioning circuits
- Pulse and step-response measurements
- ADC and DAC driver stages
- General waveform integrity and large-signal behavior
