Measure out the square footage of your personal lawn. Take notice of any obstructions, tight corners, or slopes that might also be present and make a list of them.
Call three to four professional lawn mowing services who make home visits to give estimates. Have the cost to mow your own lawn estimated -- ask about the hourly rate, total cost, and whether they charge extra for mowing around hills or other obstructions.
Compile the data and look at their costs. If one company is far lower than all the others, think about why their price might be so low. When thinking about the highest bidder, think about whether there was anything that set them apart from the others and whether that justifies the higher price.
Set a price comparable to the competition estimates but not necessarily lower. Use this as an example to draw upon when pricing other yards. Consider size, hills, obstructions, tight corners and other factors that might slow down the mowing job or make it more difficult.
Factor in the amount of gasoline that will be used while mowing. While it will not be much, larger yards will still take more gasoline than smaller ones. After filling the mower gas tank, keep track of the number of hours mowed until the next time you need to fill up. Divide the number of hours with the amount of gasoline used to get a rough estimate of the gasoline used each hour.