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Calculation Machine

NC Rating Estimate Calculator

Estimate an NC noise criterion rating from an overall dBA level.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Estimated NC rating
NC-36
Suitability
Open offices, classrooms

Quick answer

As a rough approximation, NC rating is roughly 8-10 dB below the overall A-weighted sound level for typical HVAC noise spectra.

The formula

NC ~ dBA - 9 (typical HVAC broadband spectrum approximation)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Overall sound level45 dBA

Result

  • Estimated NC ratingNC-36
  • SuitabilityOpen offices, classrooms

How to use the NC Rating Estimate Calculator

  1. 1Measure or estimate the overall A-weighted sound level in the space.
  2. 2The tool applies a typical offset to approximate the NC rating for common HVAC broadband noise.
  3. 3Use a full octave-band NC analysis for a design-grade acoustic assessment.

Frequently asked questions

Why is this only an approximation?

True NC ratings require octave-band sound pressure levels compared against NC curves; a single dBA reading cannot capture spectral shape exactly.

What NC is recommended for bedrooms?

NC-25 to NC-30 is a common target for quiet bedrooms and private offices.

About this calculator