Capacity means the maximum amount that something can hold or handle. A water bottle's capacity might be 16 ounces: that's the most it can contain before overflowing. A concert hall with a capacity of 500 people can fit exactly that many audience members safely and comfortably.

The word applies to physical space, but also to abilities and limits. When a computer's hard drive reaches full capacity, it can't store any more files. When a person works at full capacity, they're giving their maximum effort and attention. A factory running at capacity produces as many products as it possibly can with its current equipment and workers.

You might hear that a theater is filled to capacity, meaning every seat is taken. Or a teacher might say they've reached their capacity for patience, meaning they've used up all the calm they had left for the day.

Capacity differs from ability: your capacity is your maximum potential or limit, while your ability is what you can actually do. A student might have the capacity to understand advanced math, but they still need to develop the ability through practice and study. Understanding your own capacity helps you know when to push harder and when you've reached your limit.