Seed Rate Calculators

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Seed rate (seeding rate) is the amount of seed sown per unit area, expressed as kg/ha (or lb/acre) or seeds per square meter (seeds/m²). Calculating the correct seed rate ensures optimal plant population density for maximum yield — too few plants waste yield potential; too many cause competition, lodging, and may actually reduce yield. The target seed rate depends on thousand seed weight (TSW), desired plant population, expected germination percentage, and expected field establishment rate (accounting for soil conditions and pest pressure).

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Seed Rate Formula

Seed rate (kg/ha) = (target plants/m² × TSW (g) × 100) / (germination% × establishment%)

TSW = thousand seed weight (g); germination% = from seed test certificate; establishment% = expected fraction of germinated seeds that establish (typically 80–95%).

Example: wheat target 300 plants/m²; TSW = 45 g; germination 92%; establishment 90%: Seed rate = (300 × 45 × 100) / (92 × 90) = 1,350,000 / 8,280 = 163 kg/ha.

Typical Seeding Rates

  • Wheat: 100–200 kg/ha (depending on TSW and target population 200–350 plants/m²)
  • Maize/corn: 25,000–35,000 seeds/acre = 6–9 seeds/m²
  • Soybean: 60–100 kg/ha; 40–60 plants/m²
  • Rice (transplanting): 15–25 kg seed/ha for nursery; 3–6 seedlings per hill
  • Canola: 4–7 kg/ha; very small seed (TSW 3–5 g); 50–80 plants/m²

Adjusting for Germination

Seeds to sow = target plants / (germination% × establishment%) × 100. If germination = 85%: sow 100/85 = 1.18× more seeds than target plants.

Effects of Seeding Rate

Too low: reduced yield potential; excessive weed competition; poor canopy closure. Too high: inter-plant competition reduces individual plant yield components; lodging risk (cereal crops); higher seed cost. Optimum rate balances maximum biomass with minimal competition.

Glossary

Seed Rate (Seeding Rate)
Amount of seed sown per area (kg/ha or seeds/m²): rate = (target plants/m² × TSW × 100) / (germination% × establishment%); adjusted for thousand seed weight and germination.
Thousand Seed Weight (TSW)
Weight of 1,000 seeds in grams; varies by variety and lot; used to convert between seeds per m² and kg/ha: seeds/kg = 1,000,000/TSW; printed on seed certificate.
Establishment Percentage
Fraction of germinated seeds that successfully emerge as seedlings in field conditions; typically 80–95%; multiplied by germination% to calculate total seed-to-plant conversion rate.

Frequently Asked Questions

Seed rate (kg/ha) = (target plants/m² × TSW g × 100) / (germination % × establishment %). TSW = thousand seed weight in grams (from seed bag or test). Example: maize, target 8 plants/m²; TSW = 350 g; germination 95%; establishment 92%: Seed rate = (8 × 350 × 100) / (95 × 92) = 280,000 / 8,740 = 32.0 kg/ha. Divide seeds/m² by germination × establishment fraction to account for seeds that don't emerge. Higher TSW means fewer seeds per kg — always use the actual TSW from the seed lot being used.

TSW (thousand seed weight) is the weight of exactly 1,000 seeds in grams. It varies significantly within a species depending on variety, growing conditions, and seed processing. Wheat TSW typically ranges from 35–55 g; large-seeded varieties require more kg/ha to achieve the same plant density. TSW is measured on each seed lot and printed on the seed certificate. To calculate seeds per kg: seeds/kg = 1,000,000 / TSW (g). Example: TSW = 40 g → seeds/kg = 1,000,000/40 = 25,000 seeds/kg. TSW allows converting between seeds/m² and kg/ha for accurate seed purchasing and calibration of seeding equipment.

Germination % (from seed test certificate) tells you what fraction of seeds will germinate under controlled conditions. Field establishment % is lower than germination — seeds may germinate but seedlings may die due to soil crusting, disease, insects, or poor soil contact. To achieve a target of X plants/m², you must sow X/(germination × establishment) seeds/m². If germination = 90% and establishment = 90%, you achieve only 81% of the seeds sown. Seed rate = target plants / 0.81 = target × 1.23 — sow 23% more seed than target plants. Always use germination from the current seed test (>6 months old tests may not be valid).

Too low: reduced ground cover → more weed pressure (open canopy); fewer plants means each plant must produce more to achieve target yield — possible but riskier; lower photosynthetic canopy area; gaps in stand. Too high (overly dense): intraspecific competition reduces individual plant growth; in cereals: excessive tillering leads to weak, thin stems → lodging (falling over) at maturity, dramatically reducing harvestable yield; higher disease pressure (poor air circulation, dense canopy traps moisture); unnecessary seed cost. Optimal seeding rate varies by: crop; row spacing; expected weed pressure; climate; variety characteristics. Most agronomic crops have well-established optimal populations from variety trial data.