The reserve factor indicates margin to failure. The applied load multiplied by the reserve factor gives the failure load:

(5–32)

Reserve factor values greater than one indicate positive margin to failure and values less than one indicate negative margin. The values of reserve factors are always greater than zero.

The critical values of reserve factors lie between zero and one, whereas the non-critical values range from one to infinity. Whether the results are shown in numeric form or as contour plots, the non-critical values tend to be emphasized in comparison to critical values. Therefore, the inverse reserve factor is often preferred in practical use:

(5–33)

The non-critical values of range from zero to one and the critical values from that on.

The margin of safety is an alternative for the reserve factor in indicating margin to failure. The margin of safety is obtained from the corresponding reserve factor with the relation

(5–34)

A positive margin of safety indicates the relative amount that the applied load can be increased before reaching failure load. Correspondingly, a negative margin of safety indicates how much the applied load should be decreased. Margins of safety are typically expressed as percentages.