Add together all the time that you had your plant manufacturing. This is the time your plant is running and manufacturing. You can refer to items such as electric bills or employee time sheets to see when the plant started production and ended production on a given day. For example, assume your plant ran for 800 hours during the year.
Add together every day your plant had any production. For example, assume you had 100 days of production.
Divide the total hours of production by the total number of days worked to calculate production time per day. For example, 800 hours divided by 100 days equals 8 hours of production time per day.