Precision, Accuracy & Error Rate

Precision

It is proportion of the Positive classifications that were actually correct.

$$\text{Precision}=\frac{TP}{TP+FP}$$

Accuracy

It is the ration of True predictions of a model to all the Predictions.

$$\text{Accuracy}=\frac{TP+TN}{TP+FP+TN+FN}$$

Error Rate

$$\text{ER}=1-\text{ACC}$$

Note: Accuracy and Error Rate formulas stated above also work for Multi-category classifications.