How Loud Is a Weed Whacker? It Depends Which Category

Directive 2000/14/EC divides outdoor machinery into equipment subject to permissible noise limits and equipment subject to noise marking only. The split runs straight through the family of machines an English speaker would call a weed whacker, strimmer or string trimmer.

Grass trimmers and grass edge trimmers are in the marking-only group, alongside brush cutters, hedge trimmers and leaf blowers. Lawn trimmers and lawn edge trimmers are in the limit-value group, alongside lawnmowers.

The definitions that decide which is which live in Annex I of the directive. From the perspective of someone standing in a garden centre, two machines that do the same job can sit under different regimes — and only one of them has a legal ceiling on its noise.

Marking-only is not the absence of regulation. The manufacturer must still determine the guaranteed sound power level by the method in Annex III and mark it on the machine, and that figure is legally meaningful — it is a guarantee, not marketing.

What is missing is a cap. Two grass trimmers can both comply while differing substantially in declared sound power, so the marked figure becomes the only way to compare them.

It also means the marked figure is the best-documented number available for that machine. It is a declaration rather than an independent measurement, which is exactly how we label it.

A two-stroke petrol trimmer produces engine noise, exhaust noise and cutting noise together, and the engine dominates. A battery trimmer removes the engine entirely, leaving line noise, the head, and airflow — a different spectrum as well as usually a lower level.

The cutting head matters more than people expect. Line diameter and length change how much air the head moves and how hard the line strikes; a bump-feed head that has paid out too much line loads the motor and raises the noise.

What you are cutting matters too. Light grass, woody stems and a fence line all sound different, and hitting a fence or a kerb produces impulsive noise that no declared figure describes.

Most complaints about trimmers are not about level at all; they are about time of day, duration and repetition. Local noise rules generally work with permitted hours rather than decibel limits for garden equipment, precisely because a level at a boundary is difficult to enforce for a mobile machine.

That is why the EU chose to regulate the machine rather than the garden. A sound power declaration travels with the equipment; a level at a fence depends on the fence, the garden and the day.

If you want to reduce the impact on people nearby, the levers are the ones the regulation cannot reach: when you run it, for how long, and how close to a boundary.

Comparing your own machine against itself is where a phone is dependable: full throttle against idle, fresh line against a long paid-out line, cutting grass against cutting nothing.

Uncalibrated, our meter reports an A-weighted digital signal level in dBFS, which is relative rather than sound pressure. Wind across the microphone is a serious problem outdoors and adds noise that has nothing to do with the machine, so a windscreen or a sheltered position matters more than the number of decimal places.