How often does a sound level meter need to be calibrated?

It needs a field check with a sound calibrator before and after each set of measurements, and a laboratory test at the interval your regulator or standard sets. HSE's L108 asks for a verification within the previous two years, and OSHA's Technical Manual expects a certificate from the past 12 months on its compliance officers' instruments.

What is the difference between a Class 1 and a Class 2 sound level meter?

IEC 61672-1 gives both classes the same design goals. Class 2 has acceptance limits equal to or larger than class 1, and the two also differ in operating temperature range.

What is a field calibration check on a sound level meter?

You put a sound calibrator on the microphone, compare the reading with the calibrator's known level, and repeat this at the end of the measurements. It checks the meter and microphone at one frequency and one level, and HSE's L108 asks for the two readings to agree within 1 dB.

Does a sound calibrator need to be calibrated too?

Yes. OSHA's Technical Manual requires annual calibration of calibrators used for pre-use and post-use checks. IEC 60942 Annex B gives the periodic tests, which NATA lists as sound pressure level, output frequency and total distortion plus noise.

Is a sound level meter's internal calibration enough?

No. HSE's L108 says internal electronic calibration checks only the instrument's electronics and not the microphone. It can be a useful cross-check, but a sound calibrator on the microphone is what checks the two together.

Can a smartphone app replace a sound level meter?

Not for measurements that have to meet a standard. HSE's L108 says smartphone apps cannot conform to the specification standards for sound level meters, and that they can be more than 10 dB in error.

Compliance and audits

Sound level meter calibration: field checks, lab tests and Class 1 vs Class 2

11 min read Published November 9, 2026

A sound level meter gets two kinds of calibration: a field check with an acoustic calibrator before and after each set of measurements, and a periodic laboratory test to IEC 61672-3 at an interval commonly set at one or two years. The field check confirms sensitivity at one frequency and one level, while the laboratory test also covers the frequency weightings, level linearity and the rest of the meter's response.

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What does calibrating a sound level meter involve?

Two jobs share the word calibration. The first is the check you make yourself in the field. A sound calibrator puts a known tone on the microphone, and you compare the meter's reading with it before you measure and again at the end. The second is a periodic test in a laboratory, which runs a fixed set of tests against the meter's specification and issues a report. OSHA's Technical Manual calls these pre-use and post-use calibration and periodic factory-level calibration. IEC 61672-3 calls the laboratory work periodic testing.

Neither replaces the other. The field check shows that the meter and its microphone held steady on the day, at one frequency and one level. It says little about the meter's response at other frequencies or levels. Guidance L108 from the UK Health and Safety Executive (HSE) also points out that a meter's internal electronic calibration checks only the electronics and leaves the microphone out.

Field check and laboratory periodic test compared
Aspect	Field check	Laboratory periodic test
Who does it	The person taking the measurements	A calibration laboratory
When	Before and after each set of measurements	At an interval set by your regulator, your measurement standard or your own program
What it uses	A sound calibrator or pistonphone on the microphone	Reference calibrators and electrical signal sources, following IEC 61672-3
What it covers	Sensitivity at one frequency and one level, with the microphone	A limited set of key tests across frequency, level and time response
What you keep	The readings at the start and the end	A report or certificate with results and uncertainty

Which standards cover sound level meters?

The IEC 61672 series has three parts. Part 1 (IEC 61672-1:2013, edition 2) gives the performance specifications for time-weighting, integrating-averaging and integrating sound level meters. Part 2 gives the pattern evaluation tests for a model. Part 3 (IEC 61672-3:2013, edition 2) gives the periodic tests. Sound calibrators have their own standard, IEC 60942:2017 (edition 4), and its Annex B holds their periodic tests. In the United States, ANSI/ASA S1.4-2014 Part 1 is the national adoption of IEC 61672-1:2013.

Older meters were built to older documents, and the lab has to use the test method that fits. IEC 61672-3:2013 applies to meters designed to the 2013 edition of Part 1. IEC 61672-3:2006 applies to the 2002 edition. UKAS publication TPS 49 lists which method goes with which build standard, including meters made to IEC 60651 or IEC 60804. OSHA's Technical Manual still refers to Type 1 and Type 2 meters under ANSI S1.4-1983.

Tip: The periodic test is a limited set of key tests by design. IEC 61672-3 says that if evidence of pattern approval for the model is not publicly available, no general conclusion about conformance to Part 1 can be made, even when the results pass. Ask your lab what its report will state.

What is the difference between Class 1 and Class 2?

IEC 61672-1 sets two performance classes with the same design goals. They differ mainly in their acceptance limits and their operating temperature range, and a class 2 limit is equal to or larger than the class 1 limit. The limits themselves sit in tables in the paid standard and vary with frequency, so take the numbers from the published edition or your meter's data sheet.

Sound calibrators have their own classes under IEC 60942:2017. Acceptance limits are smallest for class LS and greatest for class 2. The 2017 edition removed the older names LS/C, 1/C and 2/C and added LS/M and 1/M for pistonphones, so an older certificate may use a different name.

Classes of sound level meter and sound calibrator
Instrument	Class	What it means
Sound level meter	Class 1	Acceptance limits equal to or smaller than class 2 (IEC 61672-1:2013)
Sound level meter	Class 2	Acceptance limits equal to or larger than class 1 (IEC 61672-1:2013)
Sound calibrator	Class LS	Normally used only in the laboratory (IEC 60942:2017)
Sound calibrator	Class 1	Field use, primarily with a class 1 meter (IEC 60942:2017)
Sound calibrator	Class 2	Field use, primarily with a class 2 meter (IEC 60942:2017)

Tip: For workplace noise, HSE's L108 accepts class 1 or class 2 meters (Appendix 2, Table 9). OSHA's Technical Manual treats a reading from a Type 2 meter as accurate to ±2 dBA and one from a Type 1 meter as accurate to ±1 dBA. A smartphone app is a different matter. L108 warns that apps cannot conform to the specification standards, and that they can be more than 10 dB in error.

How does frequency weighting affect calibration?

A frequency weighting shapes the meter's response across the audible range. OSHA's noise standard measures on the A scale at slow response (29 CFR 1910.95). HSE's L108 uses A-weighted levels for daily exposure and C-weighted peak for peak sound pressure. OSHA's Technical Manual describes Z weighting as an unweighted scale.

A sound calibrator produces one tone at a known level, commonly 94 dB or 114 dB at 1 kHz. A level of 94 dB is a sound pressure of 1 Pa against the reference pressure of 20 µPa, and 114 dB is 10 Pa. Because the tone sits at one frequency, a field check says nothing about a weighting at any other frequency. That is the job of the periodic test, which checks frequency weightings with acoustical and electrical signals (clauses 12 and 13 of IEC 61672-3:2013).

How to check a sound level meter with an acoustic calibrator, step by step

Use the calibrator the maker specifies for your meter and microphone, at its stated level, and confirm that both have a current laboratory calibration.
Let the meter and calibrator reach the temperature of the place you will measure. Switch both on, let them warm up and check the batteries.
Set the meter as its maker's calibration procedure says, including the level range and frequency weighting.
Seat the calibrator fully on the microphone and start the tone. With a pistonphone, correct for air pressure using a calibrated barometer.
Read the meter once the level has settled and compare it with the calibrator's level, applying any correction the maker gives.
Adjust the meter only if its maker's limits allow it. If the reading is outside those limits, do not use the meter until you have found the cause.
Record the reading, the time, the calibrator's ID and any adjustment.
Take your measurements.
Apply the calibrator again at the end, without adjusting the meter, and compare the reading with the one from the start.
If the reading has moved by more than your limit, the measurements since the first check are in doubt. Investigate the meter and calibrator, and repeat the measurements if they matter.

How close should the field check be?

The limit comes from your regulator, your measurement standard or the meter's maker. HSE's L108 asks for the reading at the end to be within 1 dB of the reading at the start (Appendix 2, paragraph 13). OSHA's Technical Manual, written for its own compliance officers, gives more detail.

Field check figures from two regulators
Source	Figure	Applies to
HSE L108, Appendix 2	End reading within 1 dB of the start reading	UK workplace noise measurements
OSHA Technical Manual, Section III, Chapter 5	Within 0.2 dB of the calibrator: no adjustment suggested	OSHA compliance officers' instruments
OSHA Technical Manual, Section III, Chapter 5	Fluctuations over 1 dB: the calibrator or the instrument may have a problem	OSHA compliance officers' instruments

Tip: OSHA's manual also tells its officers not to use equipment that fails pre-use calibration, and it requires the pre-use and post-use checks to be documented. Australia's accreditation body, NATA, requires a suitably calibrated calibrator or pistonphone to be on hand for a check before and after a set of field measurements.

What does the laboratory periodic test cover?

IEC 61672-3:2013 says the purpose of periodic testing is to assure the user that the meter conforms to Part 1 for a limited set of key tests, under the conditions of the test. Its aim is consistent testing across laboratories. The tests are listed below in the order the standard gives them.

Clause 3 sets what the lab needs first. No test goes ahead without an instruction manual for the model, whether supplied with the meter, held by the lab or published online, and the accessories the test needs must come with the meter.
The lab can state conformance when the deviations stay within the acceptance limits and the uncertainty stays within the maximum permitted, with the uncertainty evaluated at 95 percent coverage.
Send your field calibrator with the meter. The Institute of Acoustics describes the requirement as a calibrator conforming to IEC 60942, of the same class as the meter and independently calibrated within the previous 12 months.
The calibrator's own periodic tests follow IEC 60942 Annex B. NATA lists sound pressure level, output frequency and total distortion plus noise as tests to include.

Tests in IEC 61672-3:2013
Clause	Test
10	Indication at the calibration check frequency
11	Self-generated noise
12	Acoustical signal tests of a frequency weighting
13	Electrical signal tests of frequency weightings
14	Frequency and time weightings at 1 kHz
15	Long-term stability
16	Level linearity on the reference level range
17	Level linearity including the level range control
18	Toneburst response
19	C-weighted peak sound level
20	Overload indication
21	High-level stability

How often should a sound level meter be calibrated?

No single interval applies everywhere. The field check comes first and happens at each set of measurements. For the laboratory test, check what your regulator or measurement standard asks for.

Laboratory intervals stated by regulators
Where	Interval	Source
UK workplace noise	A meter or calibrator more than two years old should have passed a verification test within the previous two years	HSE L108, Appendix 2, paragraph 8
OSHA compliance officers	Annual for the meter and the acoustical calibrator. A measurement cannot support a citation without a calibration certificate from the past 12 months	OSHA Technical Manual, Section III, Chapter 5
Germany, official measurements	A verification period of two years for a sound level meter used for official purposes	MessEG and MessEV, as described by the LUBW state agency

Tip: Outside those cases, start from the maker's recommendation. OSHA's manual notes that makers typically recommend annual calibration. ILAC-G24 / OIML D 10 (2022 edition) says there is no single best practice and lists factors to weigh, such as drift, use and the results of checks. Send the meter in sooner after a drop, a failed field check or a replaced microphone.

What should the certificate and record show?

The meter's make, model and serial number, and the microphone and preamplifier it was tested with.
The class and the standard the meter was tested against, including its edition, for example IEC 61672-3:2013.
The calibrator used, with its class and certificate.
The temperature, humidity and air pressure during the test.
The result of each test with its uncertainty, and the readings before and after any adjustment.
The acceptance limits and the decision rule behind any statement of conformity.
The date, the lab and your next due date.
Your field check log for each set of measurements: the readings at the start and end, the time and the calibrator used.

Tip: ISO/IEC 17025:2017 clause 7.8.4.3 does not allow a lab to recommend a calibration interval on a certificate or label unless it was agreed with the customer. Your next due date normally comes from your own interval.

How Axiospec helps with sound level meter records

Axiospec is calibration management software. Keep the meter and its calibrator as separate instruments, each with its calibration history, its certificates and its next due date. Register the calibrator as a reference standard and pick it on the meter's calibrations. Its own record then lists the calibrations it was used on, so a calibrator found out of tolerance points you to the meters it checked.

A calibration can carry test points, each with its nominal value, tolerance and as-found and as-left readings. On an in-house calibration, a final reading outside its tolerance sets the result to Fail, and recording a pass anyway takes a written reason. An accepted Fail or Damaged result puts the meter in quarantine until a passing calibration or a manager releases it. An approved Fail, Damaged or Pass with an as-found reading out of tolerance needs an out-of-tolerance impact written, and any that is missing shows in Needs attention.

Axiospec does not test the meter or decide whether it conforms to IEC 61672. It has no separate record type for field checks, so keep your check log in your quality system or attach it to a calibration record as a file.

It is free for up to 50 active instruments. A new workspace starts with a 45-day trial of Professional, with room for 1,500 active instruments. We load your existing records for you at no charge on every plan.

Common questions

How often does a sound level meter need to be calibrated?: It needs a field check with a sound calibrator before and after each set of measurements, and a laboratory test at the interval your regulator or standard sets. HSE's L108 asks for a verification within the previous two years, and OSHA's Technical Manual expects a certificate from the past 12 months on its compliance officers' instruments.
What is the difference between a Class 1 and a Class 2 sound level meter?: IEC 61672-1 gives both classes the same design goals. Class 2 has acceptance limits equal to or larger than class 1, and the two also differ in operating temperature range.
What is a field calibration check on a sound level meter?: You put a sound calibrator on the microphone, compare the reading with the calibrator's known level, and repeat this at the end of the measurements. It checks the meter and microphone at one frequency and one level, and HSE's L108 asks for the two readings to agree within 1 dB.
Does a sound calibrator need to be calibrated too?: Yes. OSHA's Technical Manual requires annual calibration of calibrators used for pre-use and post-use checks. IEC 60942 Annex B gives the periodic tests, which NATA lists as sound pressure level, output frequency and total distortion plus noise.
Is a sound level meter's internal calibration enough?: No. HSE's L108 says internal electronic calibration checks only the instrument's electronics and not the microphone. It can be a useful cross-check, but a sound calibrator on the microphone is what checks the two together.
Can a smartphone app replace a sound level meter?: Not for measurements that have to meet a standard. HSE's L108 says smartphone apps cannot conform to the specification standards for sound level meters, and that they can be more than 10 dB in error.

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