Enter the sound pressure level in dB for each octave band. All eight bands are recommended for an accurate NR rating.
Band-by-Band Rating Margin
Full Calculation Table
| Frequency Band | Measured Level | Governing NR Curve Value | Margin |
|---|
How to Determine the NR Rating of a Space
Enter the measured or predicted sound pressure level in each of the eight standard octave bands from 63 Hz to 8000 Hz.
Click Calculate NR Rating to compare each band level against the full family of standard NR curves.
Review which single octave band determines the overall NR rating, since the rating is set by the highest curve touched by any one band, not an average.
Check the resulting NR rating against the recommended range for the space type using the noise criteria selector.
Typical Recommended NR Ranges by Space Type
| Space Type | Typical NR Range |
|---|---|
| Concert hall, broadcast studio | NR 10–20 |
| Theatre, lecture hall | NR 20–25 |
| Private office, small conference room | NR 25–35 |
| Classroom | NR 25–30 |
| Hospital patient room | NR 25–35 |
| Open-plan office | NR 35–40 |
| Restaurant, retail space | NR 35–45 |
| Mechanical / equipment room (occupied briefly) | NR 50–60 |
General design guideline ranges, broadly comparable to equivalent NC ranges. Confirm the specific target for your project against the applicable national code, ISO standard, or client specification. Use the noise criteria selector for a more detailed lookup by space type.
Understanding the NR (Noise Rating) System
The Noise Rating system is the international counterpart to North America's NC system, providing a standardized single-number description of steady background noise derived from a full octave band spectrum. Developed for broad international use, NR curves appear extensively in European, Middle Eastern, and Asian building and HVAC specifications, and Canadian engineers working on international projects, including industrial facilities designed with an industrial HVAC calculator around imported equipment, or interpreting imported specifications will frequently encounter NR targets rather than NC or RC.
How the NR Rating Is Determined
Like NC, the NR rating is found by comparing each octave band level in the spectrum against a family of standard curves, numbered across a similar range, and identifying the single highest-numbered curve that any one band touches or exceeds. This is a worst-case method: if most bands sit well within a given curve but one band reaches a higher curve, the overall rating is set by that one governing band, not an average across all eight bands. The methodology is conceptually identical to NC, though the specific curve values differ somewhat, particularly at the frequency extremes. NR sits within a broader international framework for describing and assessing noise, most notably ISO 1996-1, which defines the basic quantities used to describe environmental noise internationally, though that particular standard addresses community and environmental noise rather than the indoor room-noise NR curves used here.
NR vs. NC: Similar Concept, Different Curve Family
Because NR and NC use the same worst-case, single-band comparison logic, the two systems generally produce similar numeric ratings for a typical HVAC spectrum. However, the exact curve shapes differ between the two families, so an NR rating and an NC rating computed from the identical spectrum are not guaranteed to match exactly, especially when a spectrum has pronounced low-frequency or high-frequency content where the curve families diverge most. There is no reliable universal conversion factor between the two; the correct approach for compliance purposes is always to calculate directly from the octave band data using the specific curve family referenced by the applicable specification. Run the same spectrum through the NC curve calculator to compare both results side by side.
When to Use NR Instead of NC or RC
Use the NR system whenever the governing project specification, building code, or client requirement explicitly calls for an NR target, which is common on projects following European or ISO-based standards, or on multinational projects where the specification originates outside North America. In the United Kingdom, for example, BS 8233, the British Standard for sound insulation and noise reduction in buildings, sets its building services noise guidance directly in NR terms. For domestic Canadian projects without a specific NR requirement, NC or RC remain the more commonly referenced systems, with RC generally preferred by acoustical consultants for its more complete low-frequency quality assessment. The RC rating calculator provides that additional quality assessment layer that neither NC nor NR includes.
Addressing an NR Rating That Exceeds Target
Once the NR rating and its governing octave band are identified, the appropriate corrective measure depends on the noise source and frequency. Fan-generated low-frequency noise travelling down a duct typically calls for a duct silencer sized using the attenuator sizing calculator at the governing frequency. Excessive air velocity at diffusers or terminal units producing mid-to-high-frequency noise is addressed with the duct self-noise calculator to identify a velocity reduction target. Noise breaking through duct walls into an adjacent occupied space is assessed with the duct breakout noise calculator, an especially common check on a hospital HVAC project where a patient room's NR target leaves little margin for duct-related noise breaking in from an adjacent corridor.
Frequently Asked Questions
The Noise Rating system is an international standard for describing background noise using a single number derived from octave band sound pressure levels, widely adopted in international building and HVAC specifications outside North America. It functions similarly to NC, comparing each octave band level against a family of standard curves and reporting the rating set by the highest curve touched by any single band. Projects in Europe, the Middle East, Asia, and many other regions frequently specify NR rather than NC or RC. Use the octave band calculator first if you need to combine multiple sources into one spectrum before rating it here.
NR and NC curves are similar in concept and produce broadly comparable ratings for the same spectrum, since both use a worst-case single-band comparison against a family of standard curves. The specific curve values differ somewhat between the two systems, particularly at low and high frequency extremes, so an NR rating and an NC rating for an identical spectrum will usually be close but not always numerically identical. Because international specifications typically reference NR rather than NC, using the correct system for the applicable specification matters for compliance documentation. Compare both directly using the NC curve calculator alongside this tool.
Recommended NR ranges are similar in magnitude to equivalent NC ranges. Private offices and small conference rooms typically target NR 25 to NR 35. Open-plan offices are often designed to NR 35 to NR 40. Classrooms typically target NR 25 to NR 30. Concert halls and broadcast studios require much lower ratings, often NR 15 to NR 20 or lower. These are general design guideline ranges; confirm the specific target for your project against the applicable building code, national standard, or client specification, using the noise criteria selector for a fuller lookup by space type.
There is no exact universal conversion factor between NC and NR ratings because the two curve families have different shapes at different frequencies, so the relationship depends on which specific band is governing the rating in each system. For most typical HVAC spectra dominated by mid-frequency bands, NC and NR numbers tend to be within a few points of each other, but this is not guaranteed, especially for spectra with unusual low-frequency or high-frequency content. The reliable approach is always to calculate the rating directly from the octave band data using the correct curve family, rather than converting a number from one system into the other. Enter your band data into both this tool and the NC curve calculator to see the actual comparison for your specific spectrum.
Related Noise & Acoustics Tools
North American Noise Criteria rating
Room Criteria with quality suffix
Sum spectral sound data
Target levels by space type
Silencer insertion loss by band
Velocity-generated noise