String trimmers run at arm's length from your ears for an hour at a stretch, which makes the operator ear figure unusually honest here: the person the noise hits hardest is the buyer. The category also carries the EU's outdoor noise regime, so the declared figures, where they exist, are the best conditioned on this site outside computing.
Eleven battery models carry maker declarations, plus one gas STIHL as the contrast. At the ear the battery set runs 72.6 to 86 dB(A); guaranteed sound power runs 89 to 96 dB(A).
Two numbers, never one ranking
Every declared trimmer carries two quantities. LpA is pressure at the operator's ear. LWA is sound power, the whole machine's acoustic output, and EU directive 2000/14/EC forces a guaranteed ceiling on it, printed after a measured value and an uncertainty K. EGO's telescopic model shows why the distinction matters: measured 90 dB(A) with K of 4.9, guaranteed 95. The guaranteed number is a legal ceiling, not an average, and we never mix the two quantities in one ranking. The sound power vs sound pressure explainer has the full mechanics, and our leaf blower guide runs on the same regime.
Who declares, and where
STIHL is the category's gold standard: pressure, power, the standard (EN 50636-2-91 or IEC 62841-4-4), K values and a Declaration of Conformity in every manual, with separate rows per cutting head. Husqvarna prints both numbers directly on its US product pages, but only for the pro 500 series; its consumer 40V line omits the sound group entirely. EGO declares fully in the EU and publishes nothing for its US model numbers, so our EGO figures carry an explicit regional flag mapping the EU manual to the matching US tool.
One oddity worth a buyer's attention: STIHL's FSA 60 R manuals disagree across revisions, 81 dB(A) at the ear in the 2021 US document against 77 in the current one. Same model name, different documents, both quoted with their document numbers.
The silent American aisle
Greenworks, Ryobi, Milwaukee, DeWalt, Makita, Toro and Worx publish no noise figure for any US model we checked, across manuals and product pages. Several declare for EU siblings under different model numbers, which we refuse to map across regions. Ryobi deserves the special mention: an entire product line named Whisper Series, marketed as 72 percent quieter than gas, without one decibel on a maker page. A percentage against an unnamed baseline ranks nothing, the same rule that filed Dyson in our hair dryer guide.
What gas costs your ears
STIHL's own manual for the FS 56, its entry gas trimmer, declares 93 dB(A) at the operator's ear and 105 dB(A) of sound power under ISO 22868. Against the battery set's 72.6 to 86 at the ear, that is the difference between wearing ear protection by habit and needing it by the numbers, stated entirely in one maker's own documentation.
Buying notes
STIHL sells through dealers, so its picks anchor the ranking without an Amazon link. EGO is the category's Amazon native, and Husqvarna's pro tools cycle through official Amazon stock. EGO's own US store served us Canadian pages without dollar prices, so its entries carry no maker list price.
We did not measure any of these trimmers. Every figure is the maker's own, quoted as published, with the standard, K value and document identified wherever the maker identified them.
