Why the number is not universal
A quality value is usually a control for the encoder's quantization strength, not a standardized visual score. Two encoders can produce different file sizes and artifacts at the same nominal quality. Resizing and chroma handling also affect the result.
Start from a conservative setting and make a few comparisons. If your image contains text, fine patterns or saturated edges, it may need higher quality than a softly textured photo.
Judge images in context
Inspect the output at 100% for block artifacts and at its intended display size for overall appearance. A full-width hero image receives more attention than a small thumbnail; prioritize accordingly.
If the image is still too large, consider reducing pixel dimensions before lowering quality further. A smaller, well-framed image can look better than an oversized file with aggressive compression.
Frequently asked questions
What JPEG quality does GZ recommend?
There is no single value that fits every browser encoder or image. Use the slider as a comparison control and inspect the actual result.