When planting grass from seed on a large scale, it is important to do accurate calculations to determine the right amount of seed to use per acre. Unlike when seeding smaller areas like a home yard, the total cost of seed can change dramatically with relatively minor changes in the application rates. Take the time to plan your seeding project carefully by calculating how much grass seed per acre you will need.

Use the following formula to calculate how much grass seed to use per acre when planting:
(Area x seed rate/100) x (mix percentage) = kg per acre. 
Ask a professional at the nursery, feed store, or farm supply store where you will purchase the grass seed for the coverage rates for each type of grass in the blend you will be using. Many times these rates may be expressed in kg and square meters. For example, Kentucky bluegrass generally uses .5.7 kg per 1,000 square meters; perennial rye grass will need 3.24.0 kg per 1,000 square meters; and creeping red fescue takes 1.62.0 kg per 1,000 square meters.

Decide upon the mix of seed you will be using. In this example, we will calculate using a mix of 40 percent Kentucky bluegrass, 30 percent perennial ryegrass and 30 percent red fescue.

Plug the coverage rate number for each type of grass into the equation. For our example they would look like this:
Kentucky bluegrass
(1,000 x .7/100) x (.50) = 3.5kg per 1,000 square meters
Perennial ryegrass
(1,000 x 4.0/100) x (.30) = 12.0 kg per 1,000 square meters
Red fescue
(1,000 x 2.0/100) x (.30)= 6.0 kg per 1,000 square meters 
Convert the rates from the square meters units to a per acre unit. One acre is equal to 4,046 square meters, so simply take the amounts from Step 4 and multiply them by 4.046 (round off to 4 for demonstration purposes) to get the rate per acre. In our example you will need 14 kg/acre of Kentucky bluegrass, 48 kg/acre of ryegrass, and 24 kg/acre of fescue.

Divide the rates by 2.2 to convert them from kg/acre to pounds/acre if that is your preference.