Interactive dB Calculator
Use this tool to convert between decibels and linear ratios, or combine multiple sound/power levels.
Formula: dB = 10 × log10(P2 / P1)
Formula: dB = 20 × log10(V2 / V1)
Formula: Power ratio = 10^(dB / 10)
Formula: Voltage/current ratio = 10^(dB / 20)
Formula: Total = 10 × log10(Σ 10^(Li/10))
What is a dB calculator?
A dB calculator helps you move between linear quantities (like watts, volts, or current) and logarithmic values (decibels). Decibels are widely used in acoustics, audio engineering, radio systems, telecom, and electronics because they make very large and very small ratios easier to compare.
Instead of saying “this signal is 1,000 times stronger,” you can say “it is 30 dB higher.” That shorthand is compact, practical, and easier to combine in system budgets.
When to use 10·log10 vs 20·log10
Power quantities
Use 10 × log10() when comparing power values directly (watts, milliwatts, acoustic intensity, etc.). Example: doubling power gives roughly +3 dB.
Amplitude quantities (voltage/current/pressure)
Use 20 × log10() when comparing amplitude-like quantities measured across the same impedance. Example: doubling voltage gives roughly +6 dB.
Quick reference values
| Change | Power Ratio | Voltage/Current Ratio |
|---|---|---|
| +3 dB | ~2× | ~1.414× |
| +6 dB | ~4× | ~2× |
| +10 dB | 10× | ~3.162× |
| -3 dB | ~0.5× | ~0.707× |
| -10 dB | 0.1× | ~0.316× |
How adding dB levels works
You cannot normally add dB numbers directly unless one value dominates and you are estimating. Proper addition requires conversion to linear scale first, summing, and converting back to dB.
- Convert each level: linear = 10^(Li/10)
- Sum all linear values
- Convert back: total dB = 10 × log10(sum)
Example: 60 dB + 60 dB = 63 dB (not 120 dB). Equal independent sources add by about +3 dB.
Common mistakes to avoid
- Using 20·log10 for power ratios (use 10·log10 instead).
- Adding dB values arithmetically for independent signals.
- Comparing voltage levels without matching impedance conditions.
- Confusing relative dB with absolute units like dBm, dBV, or dB SPL.
Practical applications
Audio and acoustics
Estimate loudness changes, combine speaker contributions, and compare microphone signal levels.
RF and communications
Build link budgets quickly by summing gains and losses in dB across antennas, cables, and amplifiers.
Electronics and instrumentation
Evaluate gain stages, attenuation networks, and signal-to-noise relationships over wide dynamic ranges.
Final note
Decibels are a ratio language. Once you pick the right formula and reference, calculations become fast and intuitive. Use the calculator above to check your work and avoid common conversion errors.