Take the guesswork out of storing paint leftovers. Before you replace the lid, mark the level of the paint remaining in the can with a rubber band around the outside. Clean the rim and secure the lid tightly. Add a label with the color name, and where and when it was used, for easy reference next time.
For more on painting, consider:
What to Do with Old Paint
The Perfect Paintbrush-and How to Choose It
9 Creative Uses for Old Paint Cans