dB Converter Calculator
Convert decibels to linear ratios, convert ratios back to dB, and combine two dB levels correctly.
What This dB to Calculator Does
Decibels (dB) are logarithmic, not linear. That means normal arithmetic rules do not apply in the way most people expect. This db to calculator helps you do three practical tasks quickly:
- Convert a dB value into a power ratio and an amplitude ratio.
- Convert a ratio back into decibels.
- Combine two dB levels accurately (instead of incorrectly adding the dB values directly).
Understanding dB in Plain Language
A decibel expresses how much larger or smaller one quantity is compared with another reference quantity. Because it is logarithmic, each step in dB corresponds to multiplication, not simple addition.
Power vs. Amplitude: Why There Are Two Formulas
Use the right formula for the type of quantity you are measuring:
- Power ratio: dB = 10 × log10(P2 / P1)
- Amplitude ratio: dB = 20 × log10(A2 / A1)
Amplitude includes values like voltage, pressure, or field strength. Power includes values like watts. Since power is proportional to amplitude squared, the coefficient doubles from 10 to 20.
How to Use This Calculator
1) dB to Ratios
Enter any dB value and click Convert dB to Ratios. You will get:
- Linear power ratio (P2/P1)
- Linear amplitude ratio (A2/A1)
2) Ratio to dB
Enter either a power ratio, an amplitude ratio, or both, then click Convert Ratio to dB. Ratios must be greater than zero.
3) Combine Two dB Levels
If you have two independent sources, the total level is found by converting each dB value to linear power, summing them, and converting back to dB. This tool handles that correctly in one click.
Quick Reference Values
- +3 dB ≈ 2× power
- +10 dB = 10× power
- +20 dB = 10× amplitude
- -3 dB ≈ half power
- -6 dB ≈ half amplitude
Real-World Use Cases
This type of calculator is useful for audio engineering, acoustics, RF design, electronics labs, and measurement reporting. For example, if one amplifier setting says +6 dB, this helps you estimate the expected voltage gain quickly. If two machinery noise sources each produce 70 dB at a point, you can estimate total level without manual log math.
Common Mistakes to Avoid
- Adding dB levels directly when combining sources.
- Using the 10× formula for amplitude ratios.
- Forgetting that ratios must be positive before applying log10.
- Treating dB steps as linear percentage changes.
Final Thoughts
A good db to calculator saves time and avoids subtle mistakes in technical work. Use this page as a fast utility and a practical learning reference whenever you need accurate decibel conversions.