This post features a series of calculators to find the Root-mean-square (RMS) voltage of different waveforms. V_{RMS} can be used to compute the power in Watt or dBm.

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**How to Calculate RMS Voltage**

To use the calculators, use the drop down menu to specify one of the following:

- Peak Voltage –
**Vp** - Peak-to-peak Voltage –
**Vpp** - Average Voltage –
**Vavg**

*The units of V_{RMS} are the same as those of the input voltage.*

**Time domain samples**

Calculate the RMS value using any number of time domain samples. These samples can be used to specify an arbitrary waveform.

**DC**

Direct current is a signal level that has a fixed value and does not vary with time. The RMS voltage in this case is the same as the peak voltage. Since there is no variation, the peak to peak and average values are also the same.

**Formula**

**V _{RMS} = |Vp|**

A DC/fixed value can also be entered into the time-domain sample RMS calculator to confirm this.

DC is shown in the picture above (red line) relative to other signal types.

**Calculator**

**Sine Wave**

This is one of the most common waveforms used in RF engineering labs. Also known as a continuous wave (CW) signal. The default output from an RF signal generator is a sine wave. It is used to test various RF components such as amplifiers, filters and splitters.

**Formula**

The time varying sinusoidal waveform is

**y = Vp*sin(2 πft)**

The RMS voltage is

**V _{RMS} = Vp/(√2)**

**= Vpp/(2√2)**=

*****

*π***Vavg/(2√2)**

If there’s a DC offset **V _{DC}** , the RMS voltage is

**V _{RMS-DC} = √(V_{DC}^{2} + V_{RMS}^{2})**

**Calculator**

## Modified Sine Wave

This is the sum of two square waves, one of which is delayed 0.25 of a period relative to the other.

**Formula**

The time varying signal is given by the following equations:

**y = 0, frac(ft) < 0.25**

**y = Vp, 0.25 < frac(ft) < 0.50**

**y = 0, 0.50 < frac(ft) < 0.75**

**y = -Vp, 0.75 < frac(ft) < 1**

The RMS voltage is

**V _{RMS} = Vp/(√2)**

**= Vpp/(2√2)**=

*****

*π***Vavg/(2√2)**

If there’s a DC offset **V _{DC}** , the RMS voltage is

**V _{RMS-DC} = √(V_{DC}^{2} + V_{RMS}^{2})**

**Calculator**

## Half-wave rectified Sine Wave

**Formula**

RMS voltage is

**V _{RMS} = Vp/2**

**= Vpp/4**=

*****

*π***Vavg/2**

If there’s a DC offset **V _{DC}** , the RMS voltage is

**V _{RMS-DC} = √(V_{DC}^{2} + V_{RMS}^{2})**

**Calculator**

## Full-wave rectified Sine Wave

**Formula**

The time varying waveform is represented as

**y = |Vp*sin(2 πft)**|

RMS voltage is

**V _{RMS} = Vp/(√2)**

**= Vpp/(2√2)**=

*****

*π***Vavg/(2√2)**

If there’s a DC offset **V _{DC}** , the RMS voltage is

**V _{RMS-DC} = √(V_{DC}^{2} + V_{RMS}^{2})**

**Calculator**

**Square Wave**

**Formula**

The time varying signal is given by the following equations:

**y = Vp, frac(ft) < 0.50**

**y = -Vp, frac(ft) > 0.50**

RMS voltage is

**V _{RMS} = Vp**

**= Vpp/2**=

**Vavg**

If there’s a DC offset **V _{DC}** , the RMS voltage is

**V _{RMS-DC} = √(V_{DC}^{2} + V_{RMS}^{2})**

**Calculator**

**Triangle Wave**

**Formula**

**y= |2*Vp*frac(ft) – Vp|**

RMS voltage is

**V _{RMS} = Vp/(√3)**

**= Vpp/(2√3)**=

*****

*π***Vavg/(2√3)**

If there’s a DC offset **V _{DC}** , the RMS voltage is

**V _{RMS-DC} = √(V_{DC}^{2} + V_{RMS}^{2})**

**Calculator**

**Sawtooth Wave**

**Formula**

**y= 2*Vp*frac(ft) – Vp**

RMS voltage is

**V _{RMS} = Vp/(√3)**

**= Vpp/(2√3)**=

*****

*π***Vavg/(2√3)**

If there’s a DC offset **V _{DC}** , the RMS voltage is

**V _{RMS-DC} = √(V_{DC}^{2} + V_{RMS}^{2})**

**Calculator**

**Pulse Wave**

**Formula**

The time varying signal is given by the following equations:

**y = Vp, frac(ft) < D**

**y = 0, frac(ft) > D**

Where D is the duty cycle expressed as a percentage (%).

RMS voltage is

**V _{RMS} = √D*Vp = √D*Vpp/2**

If there’s a DC offset **V _{DC}** , the RMS voltage is

**V _{RMS-DC} = √(V_{DC}^{2} + V_{RMS}^{2})**

**Calculator**

**Phase-to-phase Voltage**

**Formula**

**y = Vp*sin(t) – Vp*sin(t-2π/3)**

**V _{RMS} = Vp*√1.5 = (Vpp/2**)*

**√(1.5)**

**Calculator**

**Frequently Asked Questions**

**Is the RMS voltage a positive or negative number?**

The Root mean square value of voltage is always a positive number. Note the definition given by the formula:

**V**_{RMS} = **√(1/n)(V _{1}^{2} +V_{2}^{2} + … + V_{n}^{2})**

where **V _{1}, V_{2}, … V_{n}** are the corresponding values of voltage. The square of each value is positive and therefore

**will be positive.**

**V**_{RMS}**References**

[1] Root-mean-square on Wikipedia

[2] Duty Cycle on Wikipedia

[3] Continuous Wave on Wikipedia

[4] Modified Sine Wave on Wikipedia