Loud enough that the figure on the housing is a two-digit number in the nineties, and that figure is not a loudness. It is a guaranteed sound power level, and understanding what it is makes the shelf comparable.
The two quantities
Sound power is a property of the machine: the total acoustic energy it radiates, independent of where you stand. This is the figure marked in an oval on the housing, required by the outdoor noise directive, and it is a guarantee rather than a measurement — the maker measures, adds an allowance, rounds up.
Sound pressure is what a microphone at a place reads, and it falls with distance. The figure a manual gives for the operator’s position is this one, and it is normally a good deal lower than the number on the housing.
Both are printed as “dB”. Treating them as the same number is the error this page exists to prevent.
Where the machine types sit
In broad terms, on the guaranteed sound power scale: robots at the quiet end by a wide margin, mains and battery mowers in the middle and close to each other, petrol mowers clearly above them, and shredders at the top of this whole niche.
The differences within a category are much smaller than the differences between categories, and they are driven by blade tip speed and deck design rather than by price.
What three decibels means
On the sound power scale, three decibels is roughly a doubling of radiated acoustic power. It is not a doubling of perceived loudness, which is a much larger step. A 93 and a 96 on two ovals is a real difference and a smaller one than the arithmetic suggests.
What the figure cannot tell you
How it sounds. A robot running at a low level for six hours and a petrol mower running high for twenty minutes are experienced completely differently, and a single A-weighted number says nothing about which is more tolerable.
How this site handles it
Machine pages here print the noise figure and name the quantity. Where a listing gives a bare number with no indication of which it is — common on the imported end of these shelves — the page says the quantity is unstated rather than assuming, because assuming would put the two in the same column.
Wherever this page and the maker’s own documentation disagree, the documentation wins. Every cutting width, cutting height, stated area, pack capacity, flow rate, head, sound level and application rate on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And the pair of quantities this page will not merge: a guaranteed sound power level is not the loudness at your ear. The figure in the oval on the housing describes what the machine radiates and is a guarantee rather than a measurement; the figure in the manual describes a pressure at a position. Both are printed as decibels. This page names which one it is reporting, and says so when the listing does not.
The questions that keep coming in
Which is quieter, battery or mains?
They are closer to each other than either is to petrol. On both, most of what you hear is the blade moving air rather than the motor, and blade noise is a function of tip speed and deck design.
Why is my neighbour’s identical mower louder?
A blunt or bent blade, a loose deck panel or a packed underside all change the sound. So does the surface: a mower on a hard drive is dramatically louder than the same machine on grass.
Last reviewed 26 September 2026