Sound Pressure Level (SPL)

Convert acoustic pressure to dB SPL, invert back to pressure, sum multiple SPL values, and estimate distance loss.

How to Use

  1. Pick a mode: Pressure → SPL, SPL → Pressure, Sum Levels, or Distance Loss.
  2. Enter values (units supported). Results update instantly.
  3. Open “Show Work” for the exact formulas and steps used.
  4. Use “Share Link” only when you want a URL that restores your inputs.
Readout
Reference pressure default: 20 µPa (air, dB SPL).
Result
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Mode
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Inputs & Settings
Choose a mode, then enter values. Tool stays deterministic and browser-based.
SPL uses RMS acoustic pressure relative to p₀ (default 20 µPa).
Standard for dB SPL in air is 20 µPa.
Show Work (step-by-step)
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Work uses base units where applicable and shows the exact log steps used.

Formulas Used

dB SPL from pressure: L = 20 · log10(p / p₀)

Pressure from dB SPL: p = p₀ · 10^(L/20)

Sum levels (same reference): L = 10 · log10(Σ 10^(Li/10))

Free-field distance loss: L₂ = L₁ − 20 · log10(r₂ / r₁)

Standard reference for dB SPL in air is commonly p₀ = 20 µPa.

FAQ

Why is SPL “20·log10” instead of “10·log10”?

SPL is based on pressure amplitude. Sound intensity/power ratios use 10·log10, but pressure is proportional to the square root of intensity, so it becomes 20·log10.

What does it mean when two sources add?

Two equal, uncorrelated sources add about +3 dB (not +6 dB). This tool uses the standard logarithmic summation.

Is distance loss always accurate?

The 20·log10(r₂/r₁) model assumes free-field conditions. Real rooms, enclosures, reflections, and absorption can change results.

Tool Info

Last updated:

Updates may include unit additions, parsing improvements for summation lists, and edge-case handling.