Seed Rate Calculator
Calculate total seed needed for a field and adjust the seeding rate for germination and purity. Works in lb per acre or kg per hectare with the formula shown.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Find the total seed needed for a field, adjusted for germination and seed purity (pure live seed).
Show the formula & steps
How the Seed Rate Calculator Works
A printed seeding rate assumes every seed is alive and clean, but real seed lots include dead seed and inert matter. This calculator corrects the target rate using pure live seed (PLS), then multiplies by your field area to give the total bulk seed to buy.
Enter your area and choose the unit system: acres with a rate in pounds per acre, or hectares with a rate in kilograms per hectare. Add the seed lot’s germination and purity percentages from the bag tag.
The Formula
Pure live seed (PLS) = germination % × purity % Adjusted (bulk) rate = target rate ÷ PLS Total seed = adjusted rate × area
Dividing by PLS raises the bulk rate so the number of seeds that actually emerge matches the agronomic recommendation.
Worked Example
You want to seed 40 acres at a target of 120 lb per acre, using a lot with 90 percent germination and 98 percent purity:
- PLS = 0.90 × 0.98 = 0.882 (88.2 percent)
- Adjusted rate = 120 ÷ 0.882 = 136.1 lb per acre
- Total seed = 136.1 × 40 = 5,442 lb
Without the PLS adjustment you would buy 4,800 lb and fall short of your target plant stand.
How Seed Quality Changes the Bulk Rate
The poorer the germination or purity, the more bulk seed you need for the same living-seed target:
| Germination | Purity | PLS | Bulk rate for 120 lb/acre target |
|---|---|---|---|
| 95% | 99% | 94.1% | 127.6 lb/acre |
| 90% | 98% | 88.2% | 136.1 lb/acre |
| 85% | 95% | 80.8% | 148.6 lb/acre |
| 75% | 90% | 67.5% | 177.8 lb/acre |
Tips for Getting the Rate Right
- Read the seed tag. Germination and purity are tested values printed on every certified seed lot.
- Use PLS for fair price comparisons. A cheaper lot with low PLS can cost more per living seed once corrected.
- Match the recommendation to your species. Drilled small grains, broadcast cover crops, and forages all have different target rates.
- Recheck old seed. Germination drops in storage, so retest carry-over seed before relying on the printed figure.
Frequently asked questions
How do I calculate how much seed I need for a field?+
Multiply your field area by the seeding rate per unit area. For 40 acres at 120 lb per acre that is 40 × 120 = 4,800 lb of seed. Adjust the rate upward for germination and purity to get the bulk amount you actually buy.
What is pure live seed (PLS)?+
Pure live seed is the fraction of a seed lot that is both pure (not chaff or other matter) and able to germinate. PLS = germination percent × purity percent. A lot with 90 percent germination and 98 percent purity is 0.90 × 0.98 = 88.2 percent pure live seed.
Why adjust the seeding rate for germination and purity?+
Recommended seeding rates assume perfect seed. Real seed lots contain dead seed and inert matter, so you must spread more bulk seed to land the target number of living plants. Dividing the target rate by the PLS fraction gives the corrected bulk rate.
What units does the seed rate calculator use?+
It supports both imperial and metric. Choose acres with a rate in pounds per acre, or hectares with a rate in kilograms per hectare. The total seed result is reported in the matching weight unit, pounds or kilograms.
Does a higher seeding rate always give a better stand?+
No. Beyond the recommended rate, extra seed competes for light, water, and nutrients, which can thin the stand, encourage disease, and waste money. Use the species and variety recommendation as your target rate and adjust only for PLS.