🌾 Grass Seed & Fertilizer Calculator
Enter your lawn area and the product's recommended application rate (found on the bag label, usually per 1,000 sq ft) to find how much you need for the whole lawn.
How much product the lawn needs
Lawn products are labelled per 1,000 sq ft, so the lawn is measured in thousands of square feet and multiplied by the rate off the bag. The bag count is that total divided by bag weight, rounded up.
pounds needed = (lawn area / 1000) x rate per 1,000 sq ft
bags = ceiling(pounds needed / bag size)The defaults - 5,000 sq ft at 4 lb per 1,000 - come to 20 lb exactly, which is one 20 lb bag with nothing spare.
Getting the rate right
The rate is the input that decides everything, and it is not one number. Seed rates depend on the species, and on whether you are starting bare soil or thickening an existing lawn:
| Seed | New lawn, per 1,000 sq ft | Overseeding |
|---|---|---|
| Kentucky bluegrass | 2-3 lb | 1-1.5 lb |
| Perennial ryegrass | 6-9 lb | 4-6 lb |
| Tall fescue | 6-8 lb | 4-6 lb |
Fertilizer is trickier, because advice is given in pounds of nitrogen while the bag holds a blend. Divide by the first number in the N-P-K analysis to get pounds of product: 1 lb of nitrogen per 1,000 sq ft from a 24-0-6 needs 100 / 24 = 4.2 lb of product. Across 5,000 sq ft that is 21 lb, so a single 20 lb bag falls just short.
Do allow a little for the spread itself. Broadcast spreaders throw an uneven pattern that only evens out when passes overlap, and the standard fix is to set the spreader to half rate and cover the lawn twice at right angles. That costs no extra product but it does need the whole quantity available before you start, so buy the bag that covers the total rather than trusting the last handful in an open sack.
Frequently asked questions
How much grass seed do I need for 5,000 square feet?
Between 10 and 40 lb, depending entirely on the seed. Kentucky bluegrass at 2-3 lb per 1,000 sq ft is 10-15 lb for a new lawn; tall fescue at 6-8 lb is 30-40 lb. Overseeding an existing lawn takes roughly half those amounts.
How do I convert pounds of nitrogen into pounds of fertilizer?
Divide 100 by the first number on the bag. A 24-0-6 is 24% nitrogen, so 4.2 lb of product delivers 1 lb of nitrogen. A 10-10-10 is only 10%, so the same 1 lb of nitrogen takes 10 lb of product.
What happens if I apply more than the rate?
With fertilizer, leaf burn - yellow or brown streaks following the wheel lines, worst in heat and on dry soil. With seed, overcrowded seedlings that grow spindly and die back. Neither gives you a thicker lawn faster.