Ditch digging costs are usually measured by the cubic yard of earth removed, so it's a good idea to know how much earth needs to be removed before you begin. You can use measurements and a calculator to help you determine how much earth will actually need to be removed.
Determine your ditch's length, width and height. If expanding or lengthening an existing ditch, use a yard stick to determine the measurements. Otherwise, check with local laws and codes to determine the appropriate size for your ditch.
Find the volume of your ditch by multiplying the length times the width times the height. Your answer will be measured in cubic yards. If your ditch turns or curves, break it down into rectangular cross sections to find the volume of each rectangle separately. Then, add the volumes together to find your total volume.
Multiply the volume by the rate per cubic yard your contractor charges to find the total cost of your ditch excavation. If your contractor charges by the hour, ask for an estimate as to how many cubic yards they can remove in one hour. Divide your volume by that number, then multiply the product of that division by their hourly rate to determine the final cost.