What Is a Seed Rate Calculator?
A seed rate calculator tells you how much seed to buy and sow for a field of a given size. It takes your target seeding rate and the area to plant, then adjusts the amount upward to account for seed that will not germinate or that is contaminated with chaff, weed seed, or inert matter. The quality adjustment is based on the Pure Live Seed (PLS) concept used in agronomy and pasture management. This tool is universal — use pounds per acre with acres, or kilograms per hectare with hectares.
How to Use It
Enter the field area and pick acres or hectares. Enter your recommended seeding rate (in lb/acre or kg/ha), the germination percentage, and the seed purity percentage from the seed tag. The calculator returns the adjusted rate per unit area and the total bulk seed you should purchase.
The Formula
First compute Pure Live Seed, the share of the bag that is actually viable, pure seed:
$$\text{PLS} = \frac{G}{100}\times\frac{P}{100}$$where \(G\) = germination % and \(P\) = purity %. Then the total bulk seed is the simple requirement divided by PLS:
$$\text{Total} = \frac{R \times A}{\text{PLS}}$$with \(R\) = seeding rate per unit area and \(A\) = field area.
Worked Example
Suppose you plant 40 acres at 120 lb/acre, with 90% germination and 98% purity. PLS is:
$$\text{PLS} = 0.90 \times 0.98 = 0.882$$The unadjusted requirement is \(120 \times 40 = 4800\) lb. Adjusting for quality:
$$\text{Total} = \frac{4800}{0.882} \approx 5442\ \text{lb}$$So you should buy about 5,442 lb of bulk seed.
FAQ
Why adjust for germination and purity? A bag of seed is never 100% viable, pure seed. Dividing by PLS ensures the live seed you actually plant per acre matches your agronomic target.
What if I do not know purity? Use the value on the seed tag, or enter 100% to ignore it. Certified seed is usually 95–99% pure.
Can I use metric units? Yes. Choose hectares and enter the rate in kg/ha; the total will be in kg.
