dB ↔ Ratio Conversion Table (Power and Voltage)
Power ratio and voltage ratio side by side from 0 dB to 120 dB, so shielding effectiveness and attenuation can be read directly as a factor.
The same dB figure means different things for power and for voltage: power is 10^(dB/10) while voltage, current and field strength are 10^(dB/20). Shielding effectiveness and attenuation are normally read as voltage ratios, power budgets as power ratios. The table shows both.
dB ↔ ratio table
| dB | Power ratio (×) | Voltage / field ratio (×) |
|---|---|---|
| 0 | 1 | 1 |
| 1 | 1.259 | 1.122 |
| 2 | 1.585 | 1.259 |
| 3 | 1.995 | 1.413 |
| 4 | 2.512 | 1.585 |
| 5 | 3.162 | 1.778 |
| 6 | 3.981 | 1.995 |
| 7 | 5.012 | 2.239 |
| 8 | 6.31 | 2.512 |
| 9 | 7.943 | 2.818 |
| 10 | 10 | 3.162 |
| 11 | 12.59 | 3.548 |
| 12 | 15.85 | 3.981 |
| 13 | 19.95 | 4.467 |
| 14 | 25.12 | 5.012 |
| 15 | 31.62 | 5.623 |
| 16 | 39.81 | 6.31 |
| 17 | 50.12 | 7.079 |
| 18 | 63.1 | 7.943 |
| 19 | 79.43 | 8.913 |
| 20 | 100 | 10 |
| 25 | 316.2 | 17.78 |
| 30 | 1000 | 31.62 |
| 35 | 3162 | 56.23 |
| 40 | 10000 | 100 |
| 45 | 31620 | 177.8 |
| 50 | 100000 | 316.2 |
| 55 | 316200 | 562.3 |
| 60 | 1×10⁶ | 1000 |
| 80 | 1×10⁸ | 10000 |
| 100 | 1×10¹⁰ | 100000 |
| 120 | 1×10¹² | 1×10⁶ |
Open the calculator → dB ↔ Ratio Converter (Power/Voltage)
Formula
Power ratio = 10^(dB/10)
Voltage ratio = 10^(dB/20)
Worth memorizing
- 3 dB = ×2 power (×1.41 voltage)
- 6 dB = ×2 voltage (×4 power)
- 20 dB = ×10 voltage, ×100 power
- 60 dB = ×1000 voltage, so 60 dB of shielding cuts the field to 1/1000
Common mistakes
- Reading 20 dB of shielding as "20 times". It is 10 times in voltage, 100 times in power.
- Using the power column for voltage. At the same dB, the voltage ratio is the square root of the power ratio.
- Adding dB where addition does not apply. Adding dB multiplies ratios, which is right for cascaded attenuation but wrong for summing several signals.
- Adding uncertainty contributions directly. Independent contributions combine as the root sum of squares (RSS).
Related calculators
Results and summaries are for reference. For certification and test reports use the latest official standard text and calibrated instrument data. Last updated: 2026-10-10