Noise Pollution Calculator
Decibels Don't Add Like Ordinary Numbers
The decibel scale is logarithmic, which means two 70 dB sound sources running together don't produce 140 dB — they produce about 73 dB. That's routinely surprising to anyone used to linear units, and it's the reason naive addition badly overstates combined noise. This calculator handles two related but distinct problems: combining multiple simultaneous sound sources into one total level, and projecting how a single source's level changes with distance.
The Formula
Level at distance (inverse square law): L₂ = L₁ − 20 × log₁₀(d₂ ÷ d₁)
The combining formula converts each decibel level back to linear sound intensity, sums those intensities, then converts the sum back to decibels — which is why doubling identical sources adds roughly 3 dB rather than doubling the number itself. The distance formula models how sound spreads outward from a point source in a free field, with intensity falling off with the square of distance.
Where This Matters
- Workplace noise compliance — combining the noise levels of multiple machines running simultaneously is standard practice for occupational noise exposure assessments.
- Community noise complaints — estimating how much a source's noise level drops by the time it reaches a property line or a neighboring residence relies directly on the inverse square law.
- Event and venue planning — predicting sound levels at different distances from a stage or speaker array helps set safe and compliant sound levels in advance.
Worked Examples
| Scenario | Result |
|---|---|
| Two sources at 70 dB each, combined | 73.01 dB |
| 70 dB + 75 dB, combined | 76.19 dB |
| Three sources: 60, 65, 70 dB, combined | 71.51 dB |
| 85 dB at 1m → level at 10m | 65.00 dB |
| 85 dB at 1m → level at 100m | 45.00 dB |
| 100 dB at 1m → level at 50m | 66.02 dB |
All values computed directly from the calculator's own formulas. The distance model assumes a free field (no reflecting surfaces or barriers), which real-world environments rarely match exactly.
How to Use This Calculator
- Choose a mode: "Combine Sound Sources" or "Sound Level at Distance."
- In combine mode, enter a comma-separated list of decibel levels (e.g. 70, 75, 68).
- In distance mode, enter the Sound Level at Source, the Source Distance, and the Target Distance.
- Select Calculate to get the combined or projected sound level.
Related Calculations
Tracking environmental impact more broadly? See the Air Pollution Index Calculator for another exposure-based reference figure.