Basic grass seed calculators take specific planting zones, grass type and yard size into account when providing an estimate as to how much product a homeowner needs to adequately seed an area. Some calculators include two estimates: one that determines the amount of seed necessary for an initial planting or bare lawn and another that determines the amount of seed needed for an existing lawn. MyHomeIdeas.com, PenningtonSeed.com and Lowes.com all offer online grass seed calculators.
Geographical planting zones determine which type of grasses grow best in each area of the country. Seed producers classify grasses as either warm or cool because of their tolerance of those climates. In many cases, a local garden store carries grass seed and seed mixes that work well in that particular location.
Grass type is also an important variable as certain seeds require more seed per square foot to properly cover or recover an area. For example, zoysia lawns typically require 1 to 2 pounds of seed to cover 1,000 square feet of lawn, while fescue can take 5 to 10 pounds to cover the same area.
Typical calculations for yard size determine its acreage or square footage. To get an accurate estimate of the area requiring seeds, the homeowner must subtract any areas not slated for seeding, such as garden space.