Weighting curves

A-, C- and Z-weighting curves adjust raw sound-pressure measurements to better reflect human hearing or to capture specific aspects of the noise. A-weighting is the default for most environmental and occupational measurements; C-weighting is used for peak measurements and very high levels; Z-weighting is flat (no weighting applied).

Octave band

Frequency [Hz]	A-Weighting	C-Weighting	Z-Weighting
8	-77.8	-17.7	0.0
16	-56.7	-8.5	0.0
31.5	-39.4	-3.0	0.0
63	-26.2	-0.8	0.0
125	-16.1	-0.2	0.0
250	-8.6	0.0	0.0
500	-3.2	0.0	0.0
1000	0	0	0
2000	1.2	-0.2	0.0
4000	1.0	-0.8	0.0
8000	-1.1	-3.0	0.0
16000	-6.6	-8.5	0.0

Third-octave band

Frequency [Hz]	A-Weighting	C-Weighting	Z-Weighting
6.3	-85.4	-21.3	0.0
8	-77.8	-17.7	0.0
10	-70.4	-14.3	0.0
12.5	-63.4	-11.2	0.0
16	-56.7	-8.5	0.0
20	-50.5	-6.2	0.0
25	-44.7	-4.4	0.0
31.5	-39.4	-3.0	0.0
40	-34.6	-2.0	0.0
50	-30.2	-1.3	0.0
63	-26.2	-0.8	0.0
80	-22.5	-0.5	0.0
100	-19.1	-0.3	0.0
125	-16.1	-0.2	0.0
160	-13.4	-0.1	0.0
200	-10.9	0.0	0.0
250	-8.6	0.0	0.0
315	-6.6	0.0	0.0
400	-4.8	0.0	0.0
500	-3.2	0.0	0.0
630	-1.9	0.0	0.0
800	-0.8	0.0	0.0
1000	0	0	0
1250	0.6	0.0	0.0
1600	1.0	-0.1	0.0
2000	1.2	-0.2	0.0
2500	1.3	-0.3	0.0
3150	1.2	-0.5	0.0
4000	1.0	-0.8	0.0
5000	0.5	-1.3	0.0
6300	-0.1	-2.0	0.0
8000	-1.1	-3.0	0.0
10000	-2.5	-4.4	0.0
12500	-4.3	-6.2	0.0
16000	-6.6	-8.5	0.0
20000	-9.3	-11.2	0.0

How we use these weightings

A-weighted levels are the basis for most of our work, from noise impact assessments under BS 4142 and BS 8233 through to noise at work assessments under the Control of Noise at Work Regulations 2005. C-weighting is required for peak-action-level measurements in occupational noise (LCpeak ≥ 135 dB(C)).