Estimate how much grass seed to buy from your lawn area, seeding rate, project type, optional buffer, and bag size.
Advanced options
How to use our Grass Seed Calculator
- Pick Lawn shape, choose Project type, and set Area unit to feet or meters.
- Enter the lawn size using Length (feet or meters) and Width (feet or meters), or enter Lawn area (square feet or square meters) if you already know it.
- Type the label rate into Seeding rate (lb per 1,000 sq ft or kg per 100 sq m). Make sure it matches your selected Project type: new lawn or overseeding.
- If you want a shopping estimate, open Advanced options and add Extra to buy (%) and Bag size (lb or kg).
- Click Calculate, then sanity-check Lawn area and Seeding rate used first. If those look right, use Grass seed needed, Grass seed to buy, and Bags to buy for your purchase plan.
Definitions
Lawn shape: The yard shape used to estimate area: rectangle, circle, triangle, ellipse, or area already known.
Project type: Whether you are seeding a New lawn on bare soil or Overseed existing lawn to thicken thin grass. New lawns often use a higher label rate than overseeding [1].
Area unit: The measurement system for the whole calculation. US mode uses square feet. Metric mode uses square meters.
Seeding rate: How much seed is applied for a standard area. In this calculator it is lb per 1,000 sq ft or kg per 100 sq m.
Extra to buy (%): An optional buffer added to the base seed amount to cover overlap, edges, or small waste.
Bag size: The weight of one seed bag in the same unit system as your result, used to estimate Bags to buy.
Common mistakes and quick fixes
Mistake: Leaving Project type on New lawn but entering an overseeding label rate, or the other way around.
Fix: Match Project type to the seed label before checking Seeding rate used .
Mistake: Typing full yard size into Length (feet or meters) but forgetting Width (feet or meters) for a rectangle.
Fix: Enter both measurements for rectangle mode, then confirm the Lawn area looks reasonable.
Mistake: Using Lawn area (square feet or square meters) while a different shape is selected and expecting that area to be used.
Fix: Choose Lawn shape = Area already known when you want the calculator to use Lawn area (square feet or square meters) .
Mistake: Entering a bag coverage number into Seeding rate (lb per 1,000 sq ft or kg per 100 sq m) instead of a true rate by area.
Fix: Read the seed label carefully and enter the rate in lb per 1,000 sq ft or kg per 100 sq m, then compare it to Grass seed needed .
Mistake: Putting 10 into Bag size (lb or kg) when the bag is 10 pounds but Area unit is metric and your rate is in kilograms.
Fix: Keep Bag size (lb or kg) in the same unit system as your selected Area unit and Seeding rate used .
Mistake: Adding a very large Extra to buy (%) without noticing how much it changes the shopping total.
Fix: Check both Grass seed needed and Grass seed to buy so you can see the effect of the buffer before buying.
Limitations & Key Assumptions / Boundary Conditions
- This calculator handles one lawn section at a time. For several sections, calculate each section separately and add the seed amounts.
- The result depends on the Seeding rate (lb per 1,000 sq ft or kg per 100 sq m) you enter. If the label rate is wrong, the answer will be wrong.
- Project type does not change the math by itself. It helps you choose the correct rate for new lawn versus overseeding.
- Shape formulas assume simple geometric sections. Irregular yards, curved borders, and beds can make the true area different.
- Extra to buy (%) is only a shopping buffer, not a turf recommendation. A bigger buffer increases Grass seed to buy but does not change the base need.
- Bags to buy is rounded up to whole bags and is shown only when Bag size (lb or kg) is entered and greater than 0.
- Results are estimates for planning. Real purchase amounts can differ because of seed coating, product blends, spreader overlap, and the exact label instructions for your grass type [2].
Methodology
How the calculator works
The calculator first finds your Lawn area from the selected shape, or it uses your entered area directly when Lawn shape is set to Area already known. Then it multiplies area by your entered Seeding rate. After that, it can add an optional shopping buffer and estimate whole bags.
Area formulas
Rectangle: A = L x W
Circle: A = pi x r^2
Triangle: A = (b x h) / 2
Ellipse: A = pi x (L/2) x (W/2)
For an ellipse, the calculator uses the full entered length and width, then halves each one inside the formula.
Seed formulas
US units: seed needed = area in sq ft x rate in lb per 1,000 sq ft / 1000
Metric units: seed needed = area in sq m x rate in kg per 100 sq m / 100
Seed to buy = seed needed x (1 + extra percent / 100)
Bags to buy = round up(seed to buy / bag size)
Worked example
Suppose your yard is a 40 by 25 foot rectangle, so the area is 1,000 square feet. If your Seeding rate is 4 lb per 1,000 sq ft, then Grass seed needed is 4 lb.
Area = 40 x 25 = 1,000 sq ft
Seed needed = 1,000 x 4 / 1000 = 4 lb
If you add Extra to buy (%) of 10, then Grass seed to buy becomes 4.4 lb. If one bag is 7 lb, then Bags to buy is 1 because the result is rounded up.
Seed to buy = 4 x 1.10 = 4.4 lb
Bags to buy = round up(4.4 / 7) = 1
Assumptions and limits
This method assumes your measurements match the chosen shape and that your entered rate already matches your selected Project type. New lawn and overseeding often use different label rates, so check the product instructions before trusting the result [1]. It also assumes bag weight is entered in the same unit system as the calculation.