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Noise Reduction Coefficient (NRC) Calculator

Calculate the Noise Reduction Coefficient (NRC) of an acoustic material from its sound-absorption coefficients at 250, 500, 1000 and 2000 Hz. NRC is the standard single-number rating quoted for ceiling tiles, panels and other treatments.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

How to use this calculator

  1. Enter the material's sound-absorption coefficient at each of the four frequencies (each between 0 and 1).
  2. Read the NRC value, rounded to the nearest 0.05, plus the raw average before rounding.
  3. Compare NRC values between products — higher means more absorptive on average across speech frequencies.

How it works

NRC is simply the arithmetic mean of the absorption coefficients at 250, 500, 1000 and 2000 Hz, then rounded to the nearest 0.05. A coefficient of 0 means fully reflective and 1 means all sound energy absorbed. Because it averages the mid-band frequencies, NRC describes how well a surface tames general room reverberation and speech-range noise.

Worked example

Worked example. A panel with coefficients 0.2, 0.4, 0.6 and 0.8 has a raw average of 0.5, giving an NRC of 0.50. Coefficients of 0.15, 0.35, 0.55 and 0.7 average to 0.4375, which rounds to an NRC of 0.45.

Common mistakes

  • Using values outside 0–1 — absorption coefficients are ratios, not percentages entered as whole numbers.
  • Forgetting the rounding step: NRC is always to the nearest 0.05, so 0.4375 becomes 0.45.
  • Treating NRC as a full spec — it ignores the 125 Hz and higher bands, so two materials with the same NRC can behave very differently.

Frequently asked questions

Can NRC be greater than 1?

Lab-measured coefficients can exceed 1 due to edge diffraction and measurement effects, so a published NRC can occasionally read above 1.00. For a quick estimate, keep inputs within 0–1.

How does NRC differ from SAA?

The newer Sound Absorption Average (SAA) averages twelve one-third-octave bands from 200 to 2500 Hz and rounds to 0.01, so it is more detailed than the four-band NRC.

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