AudioCalcs
Sound Pressure Level Calculator — Pa to dB SPL
Convert between sound pressure in pascals and SPL in decibels. Reference: 20 µPa (threshold of hearing).
How We Calculate This
SPL (dB) = 20 × log10(P / P_ref)
Where P is the sound pressure in pascals and P_ref is 20 × 10⁻⁶ Pa (20 µPa).
P = P_ref × 10^(SPL/20)
The factor of 20 (not 10) is used because SPL is a field quantity (pressure), not a power quantity.
Frequently Asked Questions
The reference pressure is 20 micropascals (20 µPa or 0.00002 Pa), which is approximately the threshold of human hearing at 1 kHz. An SPL of 0 dB corresponds to this reference pressure.
Quiet room: 30-40 dB, normal conversation: 60-70 dB, city traffic: 80-85 dB, rock concert: 100-115 dB, threshold of pain: ~120-140 dB (20-200 Pa). Prolonged exposure above 85 dB can cause hearing damage.
Human hearing spans an enormous range — from 20 µPa to 200 Pa, a ratio of 10 million to 1. The logarithmic decibel scale compresses this range into a manageable 0-140 dB scale that also better corresponds to perceived loudness.
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Last updated: February 2026
All calculations are estimates based on standard formulas. Always verify results for critical applications.