How the seeding rate is calculated
Seeding rate is not just “how many plants I want.” Not every seed germinates, not every seedling survives, and bagged seed is never 100% pure. A good seeding rate works backwards from the stand you want and adds what you expect to lose.
Pounds of seed per acre = Seeds per acre ÷ Seeds per pound ÷ Purity
Then multiply by acres for total seed, divide by pounds per bushel for bushels, and apply your price for cost. Not sure of your acres? Measure them with the acreage calculator.
Seed tag terms explained
- Germination %: share of pure seeds that sprout under ideal lab conditions.
- Purity %: share of the bag that is actually the crop seed, as opposed to inert matter, weed seed or other crops.
- Seeds per pound: seed size. Larger seeds have fewer seeds per pound and need more pounds per acre for the same population. Check the tag or count your own sample.
- Field survival / emergence: the share of germinating seed that becomes an established plant in your field. Cold, wet or crusted soil, poor seed-to-soil contact and pests lower it.
- PLS (pure live seed): purity × germination. Forage and conservation seed is often bought and priced by PLS.
Using thousand-kernel weight (TKW) or a per-square-foot target
Small-grain guides usually give the target in plants per square foot and describe seed size by thousand-kernel weight (TKW), the weight in grams of 1,000 seeds. Both work here. Enter the target per sq ft (multiply by 43,560 for plants per acre) and the TKW, and the calculator converts: seeds per lb = 453,592 ÷ TKW. For example, a TKW of 35 g is about 12,960 seeds per lb. Leave the alternate fields empty to use plants per acre and seeds per pound instead.
Crop reference values
| Crop | Target plants / ac | Seeds / lb | Germ / survival | Seeds to plant / ac | Lb / ac | Bu / ac |
|---|---|---|---|---|---|---|
| Soybeans | 140,000 | 2,800 | 90% / 90% | 172,840 | 62.4 | 1.04 |
| Corn (grain) | 32,000 | 1,400 | 95% / 95% | 35,457 | 25.6 | 0.46 |
| Wheat (winter) | 1,200,000 | 13,000 | 92% / 85% | 1,534,527 | 119.2 | 1.99 |
| Oats | 900,000 | 13,000 | 92% / 85% | 1,150,895 | 89.4 | 2.79 |
| Barley | 1,000,000 | 11,000 | 92% / 85% | 1,278,772 | 117.4 | 2.45 |
| Cereal rye | 1,000,000 | 18,000 | 90% / 85% | 1,307,190 | 74.1 | 1.32 |
| Grain sorghum | 70,000 | 15,000 | 90% / 85% | 91,503 | 6.2 | 0.11 |
Seeding rate calculator examples: wheat, corn and soybeans
Wheat seeding rate calculator: winter wheat
Target 1.2 million plants/ac; 13,000 seeds/lb; 92% germination; 85% survival; 99% purity. Seeds to plant = 1,200,000 ÷ (0.92 × 0.85) = 1,534,527 per acre. Pounds = 1,534,527 ÷ 13,000 ÷ 0.99 = 119 lb/ac (2.0 bu/ac). Open the wheat seeding rate calculator with these values loaded.
Soybean seeding rate calculator
Target 140,000 plants/ac; 2,800 seeds/lb; 90% germination; 90% survival. Seeds to plant = 172,840; pounds = 62 lb/ac (1.04 bu/ac). If soybeans are sold in 140,000-seed units, that is roughly 1.23 units per acre. Open the soybean seeding rate calculator with these values loaded.
Corn seeding rate calculator
Target 32,000 plants/ac; 1,400 seeds/lb; 95% germination; 95% survival. Seeds to plant = 35,457 per acre, about 0.44 of an 80,000-seed bag, or 26 lb/ac. The calculator shows total 80,000-seed units for your acreage. Open the corn seeding rate calculator with these values loaded, and check your stand with the plant population calculator.
Barley seeding rate calculator
Barley uses the same method as wheat: pick Barley from the crop list to load typical values (1,000,000 target plants/ac, 11,000 seeds/lb, 92% germination, 85% survival, 48 lb/bu), then adjust to your seed tag and local recommendation.
Canola, cover crops, pasture grass, peas and lentils
This seeding rate calculator also works as a canola seeding rate calculator, a pea seeding rate calculator or a lentil seeding rate calculator: choose Custom crop and enter the target population, seeds per pound and germination from your own seed tag, since these vary more by variety and region than the small grains above. A few notes:
- Canola has very small seed (a high seeds-per-pound number) and typically lower field survival than cereals, so local extension recommendations matter more than a generic default.
- Field peas and lentils are pulses and are often set by target plants per square foot with a noticeably larger seed size (fewer seeds per pound) than small grains; use your seed lot’s actual seed count.
- Grass seeding rate calculator and pasture seeding rate calculator uses: pasture and turf grasses are usually recommended as pounds of pure live seed (PLS) per acre directly, rather than a plant-population target. Enter your recommended PLS rate as the target and set purity and germination to 100% to use the calculator as a straightforward PLS-to-bulk-seed converter.
- Cover crop seeding rate calculator use: cover crop mixes combine several species at very different rates (for example, cereal rye, clover and radish in one blend), so calculate each species separately with its own seeds-per-pound and target, then add the pounds together.
When to adjust your rate
- Broadcast or poor seedbed: seed-to-soil contact is worse than with a drill, so survival is lower. Lower the field-survival value to raise the rate.
- Late planting: especially for fall-seeded small grains, later planting reduces tillering and stands, and recommendations often increase the rate.
- Low germination lots: the calculator compensates automatically: enter the tag’s germination %.
- Cover crops and forages: purpose matters (biomass, erosion control, grazing). Use a crop-specific recommendation and enter custom seed counts.
- Seed size varies by lot. Bigger seed = fewer seeds per pound = more pounds per acre for the same stand. Always use the seeds-per-pound figure for the lot you are planting.
This calculator does arithmetic. Optimal populations depend on region, variety, moisture and management, so confirm target populations with your state extension service, seed company or agronomist.
After you plant: check your stand
Verify that you achieved the population you wanted. The plant population calculator converts stand counts and seed spacing into plants per acre, and shows emergence percentage. Planning the workload? Use the farm equipment acres per hour calculator to estimate how many days you need for planting.
Frequently asked questions
How do you calculate seeding rate per acre?
Divide your target plants per acre by germination and field survival to get seeds to plant, then divide by seeds per pound and by purity to get pounds of bulk seed per acre.
How many pounds of wheat per acre should I plant?
With typical values (1.2 million target plants, 13,000 seeds/lb, 92% germination, 85% survival) the calculation gives about 119 lb/ac, or 2.0 bushels. Local recommendations vary with planting date, region and seeding method, so confirm with your extension service.
What is the soybean seeding rate per acre?
A 140,000 plants/ac target with 90% germination and 90% survival needs about 172,840 seeds/ac, or roughly 62 lb/ac at 2,800 seeds/lb. Check your seed tag for the real seeds-per-pound.
How many corn seeds per acre should I plant?
For a 32,000 plants/ac target with 95% germination and 95% survival you would plant about 35,457 seeds per acre. Many growers plant in 80,000-seed bags, so that is about 0.44 bags per acre.
Can I calculate seeding rate from plants per square foot and TKW?
Yes. Enter plants per sq ft in the alternate target field and the thousand-kernel weight in grams. The calculator converts both automatically. Seeds per lb = 453,592 ÷ TKW.
How do I convert pounds of seed to bushels?
Divide pounds by the test weight per bushel: 60 lb for wheat and soybeans, 56 lb for corn and sorghum, 48 lb for barley, 32 lb for oats.
Should I increase the seeding rate when broadcasting?
Broadcast seeding often has lower emergence than drilling because seed-to-soil contact is less consistent. Many agronomists raise the rate for broadcast seeding; enter a lower field-survival figure to model this.
Sources and further reading
The formulas on this page are standard and can be checked against these references. Where a figure is a planning range rather than a measurement, the page says so.
- Seeding Rate Calculator (UC Davis Small Grains) – target plants, thousand-kernel weight and survival
- Calculating Seeding Rates (Montana State University Extension)
- Hay and Pasture Seeding Rate Calculator (University of Wisconsin Extension) – for forage seedings
Concepts on this page: Wheat · Soybean · Maize (corn) · Seed drill · Plant density
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