This tool computes the minimum **Rise Time** of a signal from its **Bandwidth**.

It’s useful if you want to find the fastest rise time that can be measured with an oscilloscope having a certain bandwidth specification.

**Formula**

**T _{rise} = 0.35 / BW **

where

**T**is the Rise Time in Nanoseconds (_{rise}**ns**)**BW**is the Bandwidth in Gigahertz (**GHz**)

**Background**

As the bandwidth of the oscilloscope increases, the signal rise time that can be measured with it decreases. The rise time is associated with the 10-90% amplitude.

**Calculation Example**

**What is the rise time associated with a 50 MHz bandwidth?**

The calculator is used to find **T _{rise} = 0.35 / 0.05 = 7 nanoseconds**.

**What is the rise time associated with a 250 MHz bandwidth?**

Once again the calculator is used to find **T _{rise} = 0.35 / 0.25 = 1.4 nanoseconds**.

As the bandwidth of the instrument increases, the rise time measurement capability is increases. In other words, with increasing bandwidth an oscilloscope can measure faster rise times.

**What is Bandwidth?**

Within the context of an oscilloscope, bandwidth is the highest frequency of a sine wave that can be measured with at most a 3 dB error. In linear terms, the signal amplitude drops no more than 70.7% of its actual value as shown in the picture below. (Use -3 dB in the dB to linear calculator)

**Example Application**

The calculator can be used to find the minimum rise time that can be measured by an oscilloscope considering its bandwidth specification.

The DS1202Z-E oscilloscope has a bandwidth of 200 MHz. The minimum rise time is therefore 1.75 ns. The oscilloscope will not be able to measure a rise time of 1 ns for example.

*While this specification sheet confirms the 1.75 ns number, there are many oscilloscope vendors that might not include this spec – specially the cheaper ones. The calculator is useful in that case.*

**Related Calculators**

**References**

[1] Bandwidth of a signal from its rise time: Rule of Thumb #1. In this post the author derives the relationship between rise time and bandwidth empirically.

[2] How do I determine what bandwidth of scope I require for my application? An application note that estimates a 2% measurement error when the five times rule is used.