An accident frequency rate indicates the number of accidents that occurred in a company per a certain number of hours worked by all employees. The accident rate allows you to easily compare the safely in organisations having different size or over different time frames. Accident frequency rates are calculated for 100,000, 200,000 or 1,000,000 employee working hours (man-hours) depending upon the country. In North America, it is usually given per 200,000 man-hours.

Multiply the number of workers and by the number of hours they work to calculate the man-hour value. For example, if 56 men work 40 hours per week during a year (50 working weeks), then man-hours per year are 56 x 40 hours/week x 50 weeks = 112,000 hours.

Divide the number of accidents by the man-hour value to calculate the number of accidents per a working hour. For example, If the number of accidents per year is 145 then 145 / 112,000 = 0.001295.

Multiply the number of accidents per a working hour by 100,000 to calculate the accident frequency rate per 100,000 hours. In this example, the accident frequency rate is 0.001295 x 100,000 = 129.5.

Multiply the number of accidents per a working hour by 200,000 to calculate the accident frequency rate per 200,000 hours. In this example, the accident frequency rate is 0.001295 x 200,000 = 259.

Multiply the number of accidents per a working hour by 1,000,000 to calculate the accident frequency rate per 1,000,000 hours. In this example, the accident frequency rate is 0.001295 x 1,000,000 = 1295.