# Decibel Calculator

URL: https://speedycalculator.com/calculators/physics/decibel/
Last updated: 2026-10-25

> The decibel calculator converts between sound pressure and decibels, and adds two sound levels. Doubling the sound intensity adds about 3 dB, and two equal sources are 3 dB louder than one.

## Inputs

- Sound level 1 (dB)
- Sound level 2 (dB)

## Results

- Combined level
- Pressure of level 1
- Intensity ratio (1 vs 2)

## Formula

```
L = 20 log₁₀(p ÷ 20 µPa)
Combined = 10 log₁₀(10^(L₁/10) + 10^(L₂/10))
```

## Explanation

Decibels use a logarithmic scale because human hearing spans a huge range of intensities.

### How to use the Decibel Calculator

- **Sound level 1**
- **Sound level 2**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Sound levels add as intensities, so they are converted out of decibels, summed and converted back.

### Inputs explained

FieldWhat to enterSound level 1In dBSound level 2In dB

### What each result means

- **Combined level** = 10×log10(10^([Sound level 1]÷10) + 10^([Sound level 2]÷10))
- **Pressure of level 1** = 20e-6 × 10^([Sound level 1]÷20)
- **Intensity ratio (1 vs 2)** = 10^(([Sound level 1] - [Sound level 2])÷10)

### Example values

How the main result changes when **Sound level 1** changes and everything else stays at the example values above:

Sound level 1 (dB)Combined level (dB)40806080.048083.01100100.04120120160160

## Worked example

Inputs — Sound level 1: 80 dB; Sound level 2: 80 dB.

Results — **Combined level = 83.01 dB**; Pressure of level 1 = 0.2 Pa; Intensity ratio (1 vs 2) = 1 ×.

## FAQ

**Is 80 dB twice as loud as 70 dB?**
It has ten times the intensity and sounds roughly twice as loud.

**At what level does hearing damage start?**
Prolonged exposure above about 85 dB can damage hearing.

**What formula does the Decibel Calculator use?**
L = 20 log₁₀(p ÷ 20 µPa).


## Sources

- [CDC/NIOSH – Noise and hearing loss](https://www.cdc.gov/niosh/noise/)