Not be/feel up to the mark
Definition 1 of 1
Pro Tip 1/3Expectations
Used when someone doesn't live up to what was expected, either in quality or performance. 
His work today wasn't up to the mark; we expected better quality.
Pro Tip 2/3Personal State
Describes a personal feeling of not being at one's best or usual level of health or energy. 
I'm not up to the mark today; I didn't sleep well last night.
Pro Tip 3/3Subjective Standard
What is considered 'up to the mark' can vary depending on who's judging and their criteria. 
The teacher felt the essays weren't up to the mark, but the students thought differently.