Good-sized means pleasantly or satisfyingly large, but not enormous. When someone describes something as good-sized, they mean it's big enough to be useful, impressive, or enjoyable without being too much.

A good-sized bedroom gives you plenty of space to play and store your things comfortably. A good-sized serving of cake is generous and filling. A good-sized crowd at your school play means enough people showed up to make the auditorium feel alive and energetic.

The phrase suggests something is just right: substantial enough to matter. A good-sized allowance lets you save up for things you want. A good-sized backyard gives you room to run around or play catch. When your teacher assigns a good-sized project, it's big enough to be challenging and interesting without being overwhelming.

People don’t say “good-sized” about something disappointing. It's a way of acknowledging that size matters and feeling satisfied with what you've got.