When starting out it is impossible to know your costs. So you need to keep records.
I estimate by the SF. It takes out the guess work. When you start measuring you will have a property size. As you work through the season you will get data on how long it takes you to do so many SF in so much time.
Once you know the time it takes and your costs you will then get good pricing.
Example, a 1/4 acre lawn you do in 30 min's. Your costs are $20. You want to make $20 hour pay. You charge $30.
Business cost is more then gas and line and blades. Repair, maintenance, replacement money to buy new equipment. Money to add additional equipment to grow the business. Even trucks and trailers have to be factored in.
Then there is office supplies, insurance, licenses. All are part of a businesses costs.
So until you learn your costs try to find out what the local pricing is where you live so you do not ask to high and get no work or ask to low and lose money.
Many a LCO start out trying to get $60 hour. At that rate there should be enough gross to cover all of your costs and pay you a salary.