Your company is correct to calculate your leave like this. Because you work a variable shift arrangement involving longer shifts than the average 7.4 hours, you get more days off than someone working 37 hours a week Monday to Friday. For example, say you wanted a long weekend - Fri, Sat, Sun, Mon but you were only rostered to work the Friday in line with your shift pattern. You would only have to take one day's leave. Someone working Monday - Friday would have to take two day's leave for the same amount of time off. To calculate leave in hours is the fairest way if different people are working days that vary in length.