How noisy is a robot lawn mower?

Much quieter than a petrol or corded mower, but not silent, and some are clearly louder than others. Most figures quoted by manufacturers fall between the mid-50s and about 70 dB(A). As a rough guide, the low end is a gentle hum you'll barely notice indoors, and the top end is closer to a vacuum cleaner in the next room.

Some examples from manufacturers' own figures:

• Segway Navimow's original Segway Navimow H Series (H1): 54 dB(A)
• Navimow's Segway Navimow i2 LiDAR: 59 dB(A)
• Navimow's Segway Navimow X4 Series: 68 dB(A)
• Mammotion's Mammotion LUBA 3 AWD: 70 dB(A)

Be careful comparing them, because brands measure differently. Some publish a declared sound power level to the European mower standard, which includes an uncertainty margin. Others quote a lab figure taken with the blades not cutting, which flatters the result. Navimow's footnotes say its i2, H2 and X4 figures are measured without cutting load. Several brands publish no figure at all, including Mammotion for the LUBA 2 AWD.

The decibel scale is logarithmic, so a 70 dB(A) mower is far louder than a 57 dB(A) one, not just a bit. Bigger mowers with wide decks and all-wheel drive tend to be at the loud end. If you want to mow while you're in the garden, or your neighbours are close, favour a quieter model and a daytime schedule.