Decibel Calculator for Sound, Power, and Distance
This decibel calculator turns the logarithmic dB scale into plain answers: convert between decibels and ratios, combine multiple sound sources, and find how a sound level changes with distance. It is built for audio engineers, students, and anyone working with noise levels or signal gain.
Because the scale is logarithmic, a 10 dB rise means 10× more power and a 20 dB rise means 100× more — which is why 60 dB conversation and 80 dB traffic feel worlds apart. Three modes cover the most common dB tasks, and every result shows the full formula with your own numbers.
How to Calculate Decibels
Convert dB and ratios
In Converter mode, pick a direction (Ratio → dB or dB → Ratio) and a type: Power (10×log₁₀) for power or intensity, or Amplitude (20×log₁₀) for voltage or pressure. Type a value and the result appears instantly.
Add multiple sound sources
In Addition mode, enter the dB level of each source and click Add Source for more. Use the presets to fill 2 or 10 equal sources, and see the combined level from L = 10 × log₁₀(Σ10^(Lᵢ/10)).
Adjust for distance
In Distance mode, enter the known sound level, the reference distance (d₁), and the target distance (d₂). The inverse square law L₂ = L₁ − 20 × log₁₀(d₂/d₁) gives the level at the new distance.
Read the reference scale
The Sound Level Reference bar plots your result from the hearing threshold (0 dB) to the atmospheric maximum (194 dB). Any level above 85 dB shows a hearing-safety warning with the safe exposure time.
Features
Two-Way dB Conversion
Convert a ratio to decibels or decibels back to a ratio, in either direction with no extra steps.
Power & Amplitude Types
Use the 10×log₁₀ power formula for power and intensity, or 20×log₁₀ for voltage, pressure, and field quantities.
Sound Source Addition
Combine any number of sources to find the total noise level, adding or removing rows as you need.
Quick Equal-Source Presets
One click fills 2 identical sources (+3 dB) or 10 identical sources (+10 dB) to see the logarithmic effect.
Distance Attenuation
Apply the inverse square law to find the level at any distance from a known measurement point.
Real-Time Calculation
Results update instantly as you type — there is no submit button to press.
Step-by-Step Formula
Each result shows the full formula filled in with your actual values, so you can follow the math.
Sound Level Reference Bar
A color-coded gradient maps your result against everyday sounds, from a whisper to fireworks.
NIOSH Hearing Warnings
Levels above 85 dB trigger a warning with the safe exposure time from the NIOSH standard.
Frequently Asked Questions
How do you calculate decibels?
The decibel is a ratio expressed on a logarithmic scale. For power, intensity, or energy use dB = 10 × log₁₀(P₁/P₀). For voltage, sound pressure, or other amplitude quantities use dB = 20 × log₁₀(V₁/V₀). Pick the matching type in Converter mode and the calculator fills in the formula for you.
What is the difference between power dB and amplitude dB?
Power dB uses dB = 10 × log₁₀(ratio) for signal power, sound intensity, and energy. Amplitude dB uses dB = 20 × log₁₀(ratio) for voltage, sound pressure, and field strength. The factor of 20 comes from power being proportional to the square of amplitude.
Why does 80 dB + 80 dB equal 83 dB, not 160 dB?
Decibels are logarithmic, so you cannot add them like ordinary numbers. Two identical sources produce a level about 3 dB higher than one alone — so two 80 dB sources combine to roughly 83 dB. The Addition mode applies L = 10 × log₁₀(10^(L₁/10) + 10^(L₂/10)) to get the correct total.
How does distance affect the decibel level?
In free-field conditions (outdoors, no reflections), the level drops about 6 dB each time the distance from the source doubles, following L₂ = L₁ − 20 × log₁₀(d₂/d₁). Real rooms with walls and obstacles will differ from this ideal, so treat it as a close approximation.
What is the NIOSH safe exposure time?
The National Institute for Occupational Safety and Health recommends a maximum exposure based on level: 8 hours at 85 dB, halving for every 3 dB increase. That gives 4 hours at 88 dB, 2 hours at 91 dB, and about 15 minutes at 100 dB. The calculator shows this time whenever a result exceeds 85 dB.
Can decibel values be negative?
Yes. A negative dB value means the measured quantity is smaller than the reference. For example, −3 dB in power terms means the signal is half the reference power — a common result in electronics and signal processing.
What is 194 dB?
194 dB SPL is the theoretical maximum sound pressure level in Earth's atmosphere at standard conditions. Beyond it, the wave's pressure troughs would create a vacuum and it could no longer travel as an ordinary sound wave. That is why the reference bar tops out at 194 dB.
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