Decibel (dB) Calculator

Convert between decibels and linear ratios for power, voltage / amplitude, and sound pressure. Combine multiple noise sources, convert between dBm, dBW, dBu, dBV, dBFS, and consult the reference table. Everything runs in your browser — no logs, no network.

1. Ratio ↔ Decibels

A decibel is a logarithmic ratio. Power doubles every +3.01 dB; voltage / sound pressure / current doubles every +6.02 dB.

Ratio (out / in)

dB (power · 10log)

—

10 · log₁₀(P₂/P₁)

dB (field · 20log)

—

20 · log₁₀(V₂/V₁) — voltage / SPL / current

Decibels (dB)

Power ratio

—

10^{dB / 10}

Field ratio

—

10^{dB / 20}

Percent change

—

field ratio · 100% − 100%

2. Sum decibel levels (incoherent SPL combination)

Use this to combine multiple uncorrelated noise sources — e.g. two fans, two speakers playing different content, two HVAC ducts. Two equal sources add ≈ +3.01 dB; ten equal sources add +10 dB. (Coherent in-phase sources sum like voltages: two add +6 dB.)

Levels (one dB value per line; comma- or space-separated also ok)

Result

Combined level

—

10 · log Σ 10^L_i/10

Sources

—

Loudest

—

Quietest

—

Mean (energetic)

—

L_eq = total − 10 log N

Subtract background noise

Total (signal + noise), dB

Background noise alone, dB

Signal alone, dB

—

10 · log(10^T/10 − 10^N/10)

3. Absolute power references (dBm · dBW · dBµV · dBV · dBu · dBFS)

Mode

dBm

Watts

All references for the chosen dB value

dBm

—

ref 1 mW into 50 Ω (RF) / 600 Ω (audio)

dBW

—

ref 1 W (= dBm − 30)

Power

—

Voltage @ 50 Ω

—

V = √(P · 50)

Voltage @ 600 Ω

—

V = √(P · 600)

Voltage @ 75 Ω

—

V = √(P · 75)

Reference levels

Level	dB	Linear	Notes
Threshold of hearing (1 kHz)	0 dB SPL	20 µPa	Reference for sound pressure level
Quiet bedroom	30 dB SPL	—
Normal conversation @ 1 m	60 dB SPL	—
Heavy traffic / vacuum	75 dB SPL	—
NIOSH 8-hour exposure limit	85 dB SPL	—	Permissible without hearing loss
Rock concert / chainsaw	110 dB SPL	—	Pain risk after minutes
Jet take-off @ 30 m	140 dB SPL	—	Instant hearing damage
Pro audio line level	+4 dBu	1.228 V_rms	"+4" balanced; ref 0.7746 V
Consumer line level	−10 dBV	0.316 V_rms	Unbalanced RCA; ref 1 V
Mic level	≈ −40 dBu	≈ 7.75 mV	Before preamp
EBU R128 broadcast loudness	−23 LUFS	—	Integrated programme loudness
Streaming target (Spotify, YouTube)	−14 LUFS	—	Approximate
Digital full scale	0 dBFS	peak ±1.0	Anything above clips
Wi-Fi typical receive power	−65 dBm	0.32 nW	"Good" signal
Wi-Fi weak edge	−85 dBm	3.2 pW	Connection unstable
FM radio broadcast TX	+50 dBW	100 kW	= +80 dBm

Formulas

Power ratio: dB = 10 · log₁₀(P₂ / P₁) Field ratio: dB = 20 · log₁₀(V₂ / V₁) (voltage, current, SPL, particle velocity).

Sum: L_total = 10 · log₁₀(Σ 10^Lᵢ/10). Combining two uncorrelated levels of 60 dB and 60 dB gives 63.01 dB, not 120.

dBm: L = 10 · log₁₀(P / 1 mW). dBW = dBm − 30. dBV: L = 20 · log₁₀(V / 1 V). dBu: L = 20 · log₁₀(V / 0.7746 V) (ref = √(1 mW · 600 Ω)).

dBµV: L = 20 · log₁₀(V / 1 µV) — common in RF receiver sensitivity. dBFS: L = 20 · log₁₀(|x| / FS), so a sample of full scale is 0 dBFS and anything above clips.