Convert EVM percent or ratio to dB. Check modulation quality and compare link performance fast. Download a clean report as CSV or PDF anytime.
This calculator uses the standard conversion between linear EVM (RMS) and decibels.
Estimated SNR uses the common noise-limited approximation SNR(dB) ≈ −EVM(dB). It may differ for distortion-limited systems.
| EVM (%) | EVM (ratio) | EVM (dB) | Estimated SNR (dB) |
|---|---|---|---|
| 1.0 | 0.0100 | -40.0000 | 40.0000 |
| 2.0 | 0.0200 | -33.9794 | 33.9794 |
| 3.5 | 0.0350 | -29.1186 | 29.1186 |
| 5.0 | 0.0500 | -26.0206 | 26.0206 |
| 10.0 | 0.1000 | -20.0000 | 20.0000 |
EVM quantifies how far a received constellation point deviates from its ideal location across many symbols. It is usually computed as the RMS error vector magnitude divided by the RMS reference vector magnitude. Instruments may report it as a ratio or percent. Lower EVM means cleaner modulation, less impairment, and more margin for higher‑order constellations.
EVM in percent is intuitive, but dB makes comparisons easier when values span wide ranges. Because the conversion uses 20·log10(), a small improvement in EVM can appear as a clear dB change. Engineers often track EVM(dB) alongside ACPR, SNR, and noise figure.
This calculator accepts EVM as percent, a linear ratio, or directly from Vrms values. Percent and ratio are the same quantity scaled by 100. Vrms mode is useful when your instrument reports error‑vector RMS and reference RMS separately, such as during baseband verification, PA linearization, or IQ troubleshooting.
When EVM is less than 1.0 (ratio), log10(EVM) is negative, so EVM(dB) is negative too. For example, 3.5% equals 0.035, which converts to about −29.12 dB. Many teams report the magnitude |dB| for readability, but keep the sign for clarity in notes.
Target EVM depends on the modulation order, coding, bandwidth, and implementation. As a practical rule of thumb, QPSK links may tolerate several percent, 16‑QAM often aims below about 5%, 64‑QAM may target below about 3%, and 256‑QAM designs frequently push near 1–2% in good conditions. Always follow the relevant standard or device datasheet.
If errors are dominated by additive noise, EVM relates to SNR: SNR(dB) ≈ −EVM(dB). That means an EVM of −30 dB suggests roughly 30 dB SNR. Distortion, phase noise, clipping, carrier leakage, and IQ imbalance break this relationship, so treat the SNR number as a quick estimate, not a compliance metric.
Keep sample size consistent, apply the same equalization settings, and confirm your reference bandwidth. In OFDM systems, exclude guard carriers consistently and verify the measurement window. Warm up instruments, lock the clock when possible, and record the averaging method used for the final EVM. Small setup changes shift results.
Use the decimals setting to match your lab report format, then export the result block as CSV or PDF. Include the input type, EVM ratio, EVM percent, and EVM(dB) together so reviewers can reproduce the calculation. Pair the export with test conditions, frequency, power level, and equipment settings for traceability.
Most of the time, yes. When EVM ratio is below 1.0, the logarithm is negative. If EVM ratio exceeds 1.0, EVM(dB) becomes positive, which usually indicates a severely impaired or mis-scaled measurement.
Use 20·log10 for EVM because it is an amplitude ratio (RMS vector magnitude). The 10·log10 form applies to power ratios. If your value is already a power-based metric, convert it properly before using EVM formulas.
None in meaning. Percent is just the ratio multiplied by 100. For example, 2% equals a ratio of 0.02. The dB result is identical once the value is converted to a ratio.
Only roughly, and only for specific modulations and assumptions. BER depends on coding, mapping, and noise type. Use EVM to compare signal quality, then rely on standard BER curves or your system simulator for accurate BER.
Equalization can remove channel distortion and phase rotation, reducing the measured error vector. Different filter lengths, tracking loops, or pilot settings change the residual error. Always document the equalizer mode when reporting EVM.
It displays the magnitude of the dB value without the negative sign. This can be easier to read in dashboards. The raw dB value is still shown so you can keep the sign for technical interpretation.
Enter the RMS magnitude of the error vector and the RMS magnitude of the ideal reference vector. The calculator forms EVM ratio = Verr/Vref, then converts that ratio to percent and dB for consistent reporting.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.