- Choose a tab — dB Converter to convert between ratios and decibels, dB Addition to combine multiple sound sources, or SPL Reference for a chart of common sound levels.
- dB Converter: Select conversion direction (ratio→dB or dB→ratio), choose value type (power or voltage/amplitude), enter your value, and click Calculate. The tool shows the result and the exact formula used.
- dB Addition: Enter dB values for each sound source (e.g., two speakers at 85 dB and 82 dB). Click Add Source to add more. Click Calculate to see the combined total using incoherent source addition.
- SPL Reference: Browse the chart of common sound levels from the threshold of hearing (0 dB) to a rocket launch (180 dB), with color-coded danger levels.
dB (Decibel) Calculator — Your Complete Decibel Toolkit
The decibel (dB) is one of the most widely used units in engineering, acoustics, telecommunications, and audio production. Despite its ubiquity, decibel calculations are notoriously confusing because they are logarithmic, not linear. Our dB Calculator handles the three most common decibel tasks: converting between ratios and dB values, adding multiple dB sources together, and referencing real-world sound pressure levels — all computed instantly in your browser with complete privacy.
Understanding Decibels
The decibel is a dimensionless unit that expresses the ratio between two values on a logarithmic scale. It was originally developed by Bell Telephone Laboratories to measure signal loss in telephone cables and is named after Alexander Graham Bell. The logarithmic scale is used because human perception of sound intensity, light brightness, and many engineering phenomena follow a logarithmic rather than linear pattern.
Power Decibels
When comparing power quantities (watts, milliwatts, signal power):
dB = 10 × log₁₀(P₂ / P₁)
Key values: +3 dB = double the power, +10 dB = 10× the power, +20 dB = 100× the power, -3 dB = half the power.
Voltage/Amplitude Decibels
When comparing field quantities (voltage, current, sound pressure):
dB = 20 × log₁₀(V₂ / V₁)
The factor of 20 (instead of 10) accounts for the squared relationship between field quantities and power (P ∝ V²). Key values: +6 dB = double the voltage, +20 dB = 10× the voltage.
Key Features
- dB Converter: Instantly convert between ratio and dB values for both power and voltage quantities. Enter a ratio to get dB, or enter dB to get the ratio — with the exact formula displayed.
- dB Addition: Correctly add multiple dB values using the incoherent source formula. Enter 2-20+ sources and get the combined level. Essential for acoustics and noise engineering.
- SPL Reference Chart: Visual reference table of 13 common sound levels from silence (0 dB) to a rocket launch (180 dB), with color-coded danger indicators — green for safe, yellow for moderate, orange for loud, red for dangerous.
- Formula Display: Every calculation shows the exact mathematical formula used, making this a learning tool as well as a calculator.
- Calculation History: All calculations are saved locally for future reference.
Adding Decibels (Incoherent Sources)
One of the most common mistakes in acoustics is simply adding dB values together. Because decibels are logarithmic, adding two 80 dB sounds does not produce 160 dB — it produces approximately 83 dB. The correct formula for combining incoherent (uncorrelated) sources is:
L_total = 10 × log₁₀(10^(L₁/10) + 10^(L₂/10) + ... + 10^(Lₙ/10))
Practical examples:
- Two identical sources (same dB): total is original + 3 dB
- One source 10+ dB louder than others: the quieter sources have negligible effect
- Two sources differing by 3 dB: total is louder source + 1.8 dB
Common Decibel Reference Scales
dB SPL (Sound Pressure Level)
Reference: 20 micropascals (µPa), the threshold of human hearing. Used in acoustics, noise measurement, and audio engineering. Normal conversation is about 60 dB SPL, and sustained exposure above 85 dB SPL causes hearing damage.
dBm (Decibel-Milliwatts)
Reference: 1 milliwatt. Used in radio frequency engineering, fiber optics, and telecommunications. Wi-Fi signal strength is typically -30 to -80 dBm. 0 dBm = 1 mW, +30 dBm = 1 W.
dBV (Decibel-Volts)
Reference: 1 volt RMS. Common in professional audio. Line level in professional audio is typically +4 dBu (referenced to 0.775V) or -10 dBV (consumer level).
dBFS (Full Scale)
Reference: maximum digital level. Used in digital audio. 0 dBFS is the absolute maximum; all values are negative. Professional audio typically peaks at -6 dBFS to leave headroom.
Practical Applications
- Audio Engineering: Setting gain stages, calculating amplifier requirements, designing speaker systems
- Acoustics: Environmental noise assessment, workplace noise compliance, sound isolation design
- Telecommunications: Link budget calculations, signal-to-noise ratio, antenna gain
- RF Engineering: Transmitter power, receiver sensitivity, cable loss calculations
- Electronics: Amplifier gain, filter attenuation, signal processing
Privacy and Security
All calculations run entirely in your browser using JavaScript. No data is transmitted to any server. No accounts, no tracking, no data collection.