Learn Updated 2026-03-01 UTC

dB Calculator — Convert Ratios to Decibels (Educational)

Learn decibel calculations in GetCalcMaster: power vs amplitude dB formulas, common references, and verification tips.

Decibels express ratios on a log scale. This guide covers 10·log10 for power ratios and 20·log10 for amplitude ratios, plus practical sanity checks.

Open Engineering Calculator Use Notebook Guides

Important: Educational use only. dB calculations depend on whether you’re comparing power or amplitude and what reference level you’re using.

What this calculator is

The Engineering Calculator is an interactive tool inside GetCalcMaster. It’s designed to help you explore scenarios, understand formulas, and document assumptions.

Key features

Power ratio: dB = 10·log10(P2/P1)
Amplitude ratio: dB = 20·log10(A2/A1)
Know your reference (dBV, dBm, etc.)

Formula

Power ratio: dB = 10·log10(P2/P1)
Amplitude ratio: dB = 20·log10(A2/A1)
Rule: +3 dB ≈ ×2 power, +6 dB ≈ ×2 amplitude

Quick examples

P2/P1 = 10 → 10 dB
A2/A1 = 2 → 20·log10(2) ≈ 6.02 dB
P2/P1 = 0.5 → −3.01 dB

Verification tips

Use 10·log10 for power and 20·log10 for amplitude/voltage.
A negative dB value just means a ratio less than 1.
Sanity check: doubling power ≈ +3 dB; halving power ≈ −3 dB.

Common mistakes

Using 10·log10 for amplitude ratios (should be 20·log10).
Taking log of a negative value (ratios must be positive).
Forgetting reference units (dBm vs dBV vs plain dB ratios).

How to use it (quick steps)

Enter values with units (when applicable) and choose the needed formula/operation.
Use scientific notation and rounding settings that match your problem.
Evaluate and check dimensional consistency (units) and order of magnitude.
Document assumptions and results in Notebook for traceability.