Housecleaning companies generally calculate costs for cleaning commercial offices or residential homes either on a per-square-foot basis or per hour. An average cleaning time per square foot allows you to estimate the time needed for cleaning and hence the total cleaning costs if a contractor charges per hour/minute. Use a stopwatch and calculator to compute minutes of a cleaning task per square foot.

Measure the room dimensions with a measuring tape or get this information from the floor plan. For example, the room is 17.5 by 12.4 feet.

Multiply the room length and width to compute the area to be cleaned. In our example, the room area is = 17.5 feet x 12.4 feet = 217 square feet.

Set your stopwatch to the zero "0:00" time.

Start your stopwatch when cleaning begins.

Stop the timer when cleaning is complete; read the elapsed time on the stopwatch. For example, the cleaning time was four hours, 16 minutes and 30 seconds.

Convert the elapsed time to minutes using the following formula:

Time = Hours x 60 + Minutes + Seconds / 60. In our example, the time is 4 x 60 + 16 + 30 /60 = 256.5 minutes.

Divide the time by the area size in square feet to calculate the cleaning time per square foot. In our example, 256.5 minutes / 217 square feet = 1.2 minutes per square foot.