Many factors influence how well a respirator fits. Unfortunately, there are no easy measurements that determine which size of respirator is needed. Performing a fit test is the only way to determine if any respirator fits properly. There are some rough guidelines on where to start, however:

• Reusable full and half facepiece respirators are most often available in Small (S), Medium (M), and Large (L) sizes. For these respirators, a Medium will fit a majority of adult men and women (~80% of the population).
• Disposable respirators are often available in Standard, One Size Fits Most, Medium/Large (M/L), and Small (S) sizes. Standard, One Size Fits Most, and Medium/Large are often used interchangeably and will fit the majority of adults.

Remember! These are only guidelines. Once you receive your respirator, make sure it fits properly and passes fit testing requirements before using.