Sound & sleep
How to Measure Nursery Noise With Your Phone
You can't judge volume by ear in a quiet room at night. Here's how to get a real reading at your baby's mattress in five minutes.
David Nelson, Founder · 4 min read
Published · Updated
Short answer: take your baby out of the room, play the sound machine at your usual setting, and measure at the mattress, where your baby's head rests, using an app or meter set to dBA. Average for about a minute. Aim for 50 dBA or lower.
Guessing by ear doesn't work well. In a quiet room at night, your ears adjust, and a machine that feels gentle can still be louder than you think.
Step 1: Choose your tool
On iPhone: the free NIOSH Sound Level Meter app from the CDC's National Institute for Occupational Safety and Health is a strong choice. NIOSH says it's accurate within ±2 dBA, and it can be calibrated with an external microphone. [1] In a NIOSH-led study of smartphone sound apps, several iOS apps measured within ±2 dBA of professional equipment. [2]
On Android: NIOSH's app is iOS-only. NIOSH says it can't currently verify Android app accuracy. [1] The same study found Android apps varied widely from phone to phone, because manufacturers use different microphones and audio parts. [2] You can still use an Android app to compare before and after on the same phone, such as "Did moving the machine lower the level?", but treat the exact number with caution.
Most accurate: an inexpensive handheld sound level meter that offers A-weighting (dBA). Basic models are inexpensive and give you a consistent reference.
Step 2: Set up the room
- Take your baby out of the room. Never leave a phone or meter in the crib with your baby.
- Set the room up as it is at night: door closed or open as usual, fan or air conditioning on if you normally use it.
- Turn the sound machine on at your usual volume and sound.
Step 3: Take the reading
- Set the app or meter to A-weighting (dBA) and slow response, if those options exist.
- Place the phone flat on the mattress where your baby's head goes, with the microphone uncovered. The microphone is usually on the bottom edge.
- Step back so your body doesn't block or reflect the sound.
- Watch for 30 to 60 seconds and note the average. Many apps show this as "Leq" or "average." Don't use the momentary peak.
Step 4: Read the result
| Reading at the mattress | What it means | What to do |
|---|---|---|
| Under 40 dBA | Quiet | Fine, if it still masks noise for your baby |
| 40 to 50 dBA | Within the range commonly recommended | Keep it here |
| Over 50 dBA | Above the hospital nursery benchmark used in research [3] | Lower the volume or move the machine farther away, then re-measure |
Step 5: Measure the noise you're trying to cover
Turn the machine off and measure again while the household noise happens: a sibling in the hallway, the dog, the TV in the next room. This shows you how much masking you actually need. Often it's less than you'd think.
Tips for a better reading
- Re-measure after changes: a new spot, a new sound or a rearranged room.
- Use the same phone each time, so your comparisons are fair.
- Expect some wobble. Readings jump around; the average is what matters.
- Don't measure up against the machine. That number is much higher than what reaches the crib.
Frequently asked questions
Why dBA instead of dB? A-weighting adjusts the reading to match how human ears hear different pitches. It's the standard for environmental and workplace noise measurements. [4]
My app says 55 dBA. Is my baby's hearing damaged? A reading above 50 dBA doesn't mean harm has happened. It means you should turn it down or move the machine. If you're worried about your child's hearing, talk to your pediatrician.
Do I need to measure every night? No. Measure once when you set up, then again whenever something changes.
How the ARC is designed to help
Measuring by hand works, but most parents measure once and never again. The Selah ARC System, now in development, puts a sensor near the crib that measures continuously and adjusts the speaker to hold a 50 dBA hourly-average target, measured at the crib. Follow the build.
This article is general information, not medical advice. Phone readings are estimates and vary by device.
Sources
- CDC/NIOSH. NIOSH Sound Level Meter app.
- Kardous CA, Shaw PB. Evaluation of smartphone sound measurement applications. Journal of the Acoustical Society of America. 2014;135(4):EL186–EL192. doi:10.1121/1.4865269
- Hugh SC, et al. Infant sleep machines and hazardous sound pressure levels. Pediatrics. 2014;133(4):677–681.
- Wikipedia. A-weighting.
The ARC in development