How long should a reply to a Google review be?

Short answer

Short — usually two to four sentences. Long enough to feel personal and address the point, short enough that people actually read it. Walls of text read as defensive or corporate.

A good structure

• A thank-you or acknowledgment.
• One specific line about what they raised.
• A next step or warm close.

For a glowing review, a couple of warm sentences is plenty. For a complaint, resist the urge to defend yourself at length — brevity reads as confidence, and the detailed resolution belongs offline anyway.