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Decibel Ratio Calculator

Compare two positive same-kind quantities in decibels with an explicit field or power basis. Returns a ratio—not SPL, loudness, exposure, or safety.

Use this result well

Inputs that matter
Two positive same-kind quantities in the same unit, with the first declared as reference and an explicit field-quantity or power-quantity basis
Output to expect
Comparison/reference ratio, signed decibel ratio, selected basis and only the conditional square-law equivalent ratio
How it works
Use 20 log₁₀ for an appropriate field-quantity ratio or 10 log₁₀ for a power-quantity ratio while preserving the declared reference
  • Confirm that both values share the same physical quantity, unit, scaling, impedance/context, bandwidth, weighting and measurement definition before comparing them.
  • Do not relabel this relative ratio as absolute SPL, dBFS, perceived loudness, audibility, exposure or safety evidence; those require their own references, models and measurements.

Choose your path

Built around the job you need to finish

Compare two positive same-kind quantities with an explicit field or power logarithmic basis while preserving the reference and refusing SPL, loudness, exposure or safety conclusions.

Audio technician comparing two field readings

Convert one source-led same-unit amplitude ratio to dB without hiding the reference.

Enter the reference and comparison values, choose field quantity only when the square-law relationship applies, and retain both values with the signed result.

Gets an auditable ratio and does not call it an absolute calibrated level.

Engineer comparing two power values

Use the correct power-ratio convention and keep direction visible.

Select power quantity, enter positive same-kind values in the same unit, and review comparison/reference plus the signed dB result.

Avoids the factor-of-two formula error and can reproduce the calculation.

Reviewer guarding against hearing claims

Distinguish relative arithmetic from SPL, loudness and exposure evidence.

Inspect the selected basis, reference, conditional equivalent and limitation copy, then obtain the separate calibrated measurement or psychoacoustic/safety method required.

Rejects unsupported “twice as loud” and “safe” labels.

Authoritative checks for this tool

Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.

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Projects using Decibel Ratio Calculator

This tool is part of these guided projects. Each project provides step-by-step instructions with checklists and all the tools you need in one place.

Plan a Listening Room

Carry one listening-room brief from measured geometry and band-specific acoustic assumptions through equipment and copper-loop planning, safe installation, real measurements, accessibility review, and named acceptance.

6 steps3 toolsStart project

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Reference & details

How it works

Declare the quantity kind

Use the field basis only for same-kind field quantities whose squared magnitudes correspond to power under the relevant conditions. Use the power basis for same-kind power or energy quantities.

Field: 20 log₁₀(Q₂/Q₁); power: 10 log₁₀(Q₂/Q₁)

Keep the reference visible

The first entered quantity is the reference and the second is the comparison. Both must be positive and use the same unit, scaling, impedance context, and measurement definition.

Ratio = comparison quantity ÷ reference quantity

Read only the stated equivalence

The result may show the equivalent power ratio for a field ratio, or field ratio for a power ratio, under the stated square-law relationship. It does not establish SPL, perceived loudness, audibility, exposure, or compliance.

Power ratio = field ratio²; field ratio = √power ratio

Updated: August 2026

Example Scenarios

Reference 1 and comparison 2 on the field basis produce +6.0206 dB and a conditional equivalent power ratio of 4.

Reference 100 and comparison 50 on the power basis produce −3.0103 dB. The negative sign records that the comparison is below the reference.

A microphone voltage ratio alone is not an absolute sound-pressure level. Preserve calibration, reference pressure, weighting, bandwidth, time weighting, position, and uncertainty outside this ratio tool.

Common Mistakes to Avoid

Selecting field or power from the unit label alone

Confirm the physical relationship, reference, impedance/context, and measurement definition. The same-looking unit label does not supply that evidence.

Calling a ratio result SPL, loudness, or safety evidence

Keep the output labeled as a relative dB ratio and retain the separate calibration, measurement, psychoacoustic, or compliance record required for those conclusions.

FAQ

Power-like quantities use 10 log₁₀ of the ratio. Field quantities can use 20 log₁₀ when the associated power is proportional to the square of that field quantity under the relevant conditions.

No. Convert them to the same unit and confirm they describe the same physical quantity and measurement basis before calculating a ratio.

Not here. It means the entered comparison equals the entered reference. Absolute systems such as dB SPL or dBFS require their own defined references and measurement rules.

No. Loudness requires a separate psychoacoustic model and inputs. This tool returns only the declared mathematical ratio.

No. It does not measure sound pressure, exposure duration, frequency weighting, peaks, dose, or applicable limits. Use calibrated instruments and the relevant workplace, venue, or product procedure.

About Decibel Ratio Calculator

A decibel result is meaningful only when its two quantities, reference, and logarithmic basis are stated. Enter two positive quantities of the same kind and choose field quantity for amplitude-like values or power quantity for power-like values. The calculator preserves the ratio and sign; it does not invent an absolute reference or a hearing judgment.