A Class 1 sound level meter is a precision instrument. It has tighter accuracy tolerances and a wider frequency range than a Class 2 meter, and it’s required for environmental noise assessments, building acoustics and many legal or contractual measurements. A Class 2 meter is the general-purpose workhorse. For compliance, readings are generally treated as accurate to about ±2 dBA versus ±1 dBA for Class 1, and it’s accepted for most workplace noise surveys. Most national standards permit at least a Class 2 instrument.
If you’re only checking how loud your own environment is, you need neither. A phone app will do.
What do Class 1 and Class 2 mean? #
The classes come from IEC 61672, the international standard for sound level meters. It defines two performance classes. The older American standard used “Type 1” and “Type 2,” and you’ll still see both terms. They map roughly onto each other.
Both classes measure the same things: sound level with frequency weighting (A, and often C and Z) and time weighting (Fast, Slow, sometimes Impulse). The difference is how tightly the instrument must meet the specification and across what range of frequencies and conditions.
| Class 1 | Class 2 | |
|---|---|---|
| Also called | Type 1, precision | Type 2, general purpose |
| Accuracy for compliance | About ±1 dBA | About ±2 dBA |
| Frequency range | Wider, with tight tolerances at very low and high frequencies | Narrower; tolerances loosen at the extremes |
| C-weighting | Required | Common, not always required |
| Typical uses | Environmental noise, building and room acoustics, legal and consulting work, product noise | Workplace noise surveys, general-purpose checks, ordinance screening where allowed |
| Cost | Higher | Lower |
The accuracy figures are the working values commonly quoted for compliance measurements. The standard itself sets detailed tolerance limits that vary by frequency and test.
When do you need a Class 1 meter? #
- Environmental noise assessments, such as road, rail, industrial or wind turbine noise at homes, when the governing rules or permit call for Class 1.
- Building acoustics: sound insulation between apartments, facade tests, room acoustic measurements. These often need octave or third-octave band analysis, which usually comes with Class 1 instruments.
- Legal disputes and expert witness work, where the other side will challenge every decibel.
- Product and machinery noise declarations where a test standard specifies Class 1.
- Low-frequency problems, such as hum, rumble or bass complaints, where Class 1’s tighter low-frequency tolerances matter.
When is Class 2 good enough? #
- Workplace noise surveys. Many occupational noise surveys use Class 2 meters and personal noise dosimeters, which is typically what the rules allow. See noise dosimeter vs sound level meter and NIOSH vs OSHA noise limits.
- Screening measurements to find out whether a proper Class 1 assessment is needed.
- Venue, event and facilities monitoring, keeping an eye on levels during a show or across a site.
- Ordinance enforcement, where the local rule accepts Class 2. Some do and some don’t, so check the text.
What about uncertified meters and phone apps? #
Below Class 2 sits everything else: inexpensive handheld meters with no class certification, and phone apps. Some are decent, but none carries a guaranteed accuracy.
NIOSH’s research gives a sense of scale. In its 2014 study, the best iOS apps came within about 1 dB of a reference system, though most apps screened didn’t qualify for testing. NIOSH’s own SLM app meets Type 2 requirements of IEC 61672-3 only when paired with a calibrated external microphone. With the phone’s built-in mic, NIOSH quotes ±2 dBA from its lab testing.
For personal use, such as deciding when to wear earplugs, comparing rooms or keeping a noise diary, a phone app is enough. Sound Meter dB is a free option for that on iPhone and Android. It gives A-weighted or flat readings, Fast or Slow response, a proper Leq, and NIOSH-based safe-exposure time, and it states that it’s not a substitute for a Class 1 or Class 2 meter. See sound meter app vs SPL meter.
What else matters when buying a sound level meter? #
Calibration. Any class of meter should be checked with an acoustic calibrator before and after each measurement session, and both meter and calibrator need periodic lab calibration with a certificate. A Class 1 meter with a lapsed calibration certificate won’t survive scrutiny.
Integrating vs non-integrating. An integrating meter calculates Leq over time. For anything beyond a spot reading, you want one. See what is Leq.
Frequency analysis. Octave and third-octave band filters show which frequencies dominate, which matters for hearing protector selection, noise control design and low-frequency complaints.
Data logging. Long-term logging with timestamps is essential for environmental and neighbor noise work.
Weighting and time options. Make sure the meter offers the weightings and responses your rules specify. For example, OSHA’s permissible exposure table is based on A-weighted, Slow-response readings. See fast vs slow response.
Rental. Certified instruments are expensive. If you need one measurement, renting from a test-equipment company or hiring an acoustic consultant is often cheaper than buying.
Which one should you choose? #
| Your situation | What to use |
|---|---|
| Checking your own home, concert, gym or workshop | A phone app |
| Keeping a neighbor noise log | A phone app for the log; the authority measures if needed |
| Screening a workplace for noise above 85 dBA | Class 2 meter, or an app to decide where to measure properly |
| Formal workplace noise monitoring | Class 2 meter and dosimeters, used by trained staff |
| Environmental or planning assessment | Class 1, as specified in the rules |
| Building acoustics or legal expert work | Class 1 with band analysis and calibration records |
Frequently asked questions #
Is Type 1 the same as Class 1? #
Roughly. “Type 1” and “Type 2” come from the older ANSI standard in the U.S., while “Class 1” and “Class 2” come from the international IEC 61672 standard. Modern meters are usually specified to IEC 61672 classes, and people often use the terms interchangeably.
How much more accurate is a Class 1 meter than Class 2? #
For compliance purposes, Class 1 readings are commonly treated as accurate to about ±1 dBA and Class 2 to about ±2 dBA. The bigger practical differences show up at very low and very high frequencies, where Class 2 tolerances are much looser.
Can I use a Class 2 meter for OSHA noise monitoring? #
Class 2 meters and personal dosimeters are widely used for occupational noise monitoring. Check the specific requirements that apply to your workplace and make sure the instrument is calibrated and used according to procedure.
Is a phone app a Class 2 meter? #
No. A phone app isn’t certified to either class. NIOSH says its SLM app meets Type 2 requirements of IEC 61672-3 only when used with a calibrated external microphone.