Compare two positive same-kind quantities in decibels with an explicit field or power basis. Returns a ratio—not SPL, loudness, exposure, or safety.
A quick decision brief for this specific tool
Two positive same-kind quantities in the same unit, with the first declared as reference and an explicit field-quantity or power-quantity basis
Comparison/reference ratio, signed decibel ratio, selected basis and only the conditional square-law equivalent ratio
Use 20 log₁₀ for an appropriate field-quantity ratio or 10 log₁₀ for a power-quantity ratio while preserving the declared reference
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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.
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.
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.
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.
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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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)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 quantityThe 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 ratioUpdated: August 2026
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.
Confirm the physical relationship, reference, impedance/context, and measurement definition. The same-looking unit label does not supply that evidence.
Keep the output labeled as a relative dB ratio and retain the separate calibration, measurement, psychoacoustic, or compliance record required for those conclusions.
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.