What is TSW and where do I find it?

TSW (thousand seed weight) is the weight of exactly 1,000 seeds in grams. It is the most accurate measure of seed size. Weigh 1,000 seeds from the actual lot using a precision balance for the most reliable result.

Difference between germination and emergence?

Germination is the percentage that sprout under ideal lab conditions. Emergence is the percentage that produce seedlings at the soil surface in actual field conditions. Emergence is always lower by 5-20% depending on seedbed quality and temperature.

How to calibrate a seeder accurately?

Run at field speed over a measured distance covering at least 0.1 ha. Collect seed from all rows and weigh. Calculate actual kg/ha and adjust. Repeat until within 5% of target.

Seeding Rate Calculator — Free Agriculture Calculator

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Canola goes in Monday. The agronomist has given you the target plant population, the lab sent through germination, and TSW is on the bag tag. You need kg/ha before the seeder calibration starts.

Seeding Rate Calculator

Cropping

Target plant population (plants/m²)

Wheat: 150–200 · Barley: 130–180 · Canola: 40–60

Thousand grain weight — TGW (g)

From seed test certificate — typically 25–50g

Germination (%)

From seed test — typically 85–98%

Field establishment (%)

Allow 80–90% for good conditions

Paddock area (ha)

Seed rate (kg/ha) = (Plants/m² × TGW g) ÷ (Germination% × Establishment% × 1000) Target populations (plants/m²): Wheat 150–200 · Barley 130–180 · Canola 40–60 · Lupins 40–70 · Chickpeas 30–45
TGW varies year to year — always use current season's seed test. A 5g difference in TGW changes seed rate by ~15%.

Reference: GRDC — Grains Research & Development Corporation · NSW DPI — Grains

ℹ️ Results are estimates for planning purposes. Verify with current standards and a qualified professional.

1 What this calculator does

Calculates seeding rate in kg/ha from target plant population, thousand seed weight (TSW) and germination percentage. Outputs total seed for the paddock. Also reverse-calculates actual plant population from a known seeding rate.

2 Formula & professional reasoning

Seeding rate (kg/ha) = (Target plants/m2 x TSW g) / (Germination% x 10)
Total seed (kg) = Rate x Area (ha)

TSW links plant biology to the physical seed lot — canola TSW ranges 3.5-6 g between varieties and seasons. The division by 10 converts units correctly. In well-prepared seedbeds, germination approximates establishment. In poor or dry seedbeds, multiply germination by an emergence factor of 0.80-0.85.

3 Worked examples

⚠️ Illustrative example only — not clinical or professional instruction.

Basic

Canola from bag tag

Given: Target: 50 plants/m2 | TSW: 4.5 g | Germination: 92% | Area: 320 ha

Working: Rate: (50 x 4.5) / (0.92 x 10) = 225 / 9.2 = 24.5 kg/ha | Total: 24.5 x 320

Answer: 24.5 kg/ha — 7,836 kg total seed

💡 Order 8,000 kg to allow for seeder calibration waste and end-of-run overflow.

Standard

Wheat with emergence factor — dry autumn

Given: Target: 180 plants/m2 | TSW: 42 g | Germination: 95% | Emergence factor: 0.85 | Area: 500 ha

Working: Rate: (180 x 42) / (0.95 x 0.85 x 10) = 7,560 / 8.075 = 93.6 kg/ha | Total: 93.6 x 500

Answer: 93.6 kg/ha — 46,800 kg total

💡 In cloddy or dry seedbeds add emergence factor 0.80-0.85. Skip it only in perfect seedbed conditions.

Advanced

Back-calculating plant population from known rate

Given: Rate: 80 kg/ha wheat | TSW: 38 g | Germination: 96%

Working: Population: (80 x 0.96 x 10) / 38 = 768 / 38

Answer: 20.2 plants/m2 — well below 150-200 target

💡 20 plants/m2 is far below target. Most likely cause: TSW entered as 380 instead of 38 g. Recheck inputs before sowing.

4 Sanity check

Typical target populations

Canola: 40-80 plants/m2 | Wheat: 150-200 | Barley: 120-180 | Lentils: 100-130

Check with agronomist for variety-specific and paddock-specific targets.

Typical TSW by crop

Canola: 3.5-6 g | Wheat: 30-50 g | Barley: 40-60 g | Lentils: 50-80 g

Always measure TSW from the actual lot — same variety can vary 20% between seasons.

Germination test validity

Use most recent test | Most seed stores 6-12 months

Re-test seed stored more than 12 months before committing to a seeding program.

Seeder calibration

Calibrate over 1 ha of actual paddock — not a short test run

Short runs consistently overestimate actual rate due to flush at startup.

5 Common errors

Error	Cause	Consequence	Fix
Variety average TSW instead of measured lot	Not testing the actual seed on hand	Rate off by 20-40% — population target missed	Weigh 1,000 seeds from the actual lot. Variety averages vary significantly between seasons.
No emergence factor in poor seedbed	Assuming germination equals establishment	Population 15-20% below target — yield penalty	Dry, cloddy or cold seedbeds: multiply germination by emergence factor 0.80-0.85.
Not calibrating seeder after changing seed lot	Assuming same flow characteristics	Wrong population established	Different lots have different sizes and coatings. Always calibrate with the actual lot.
No allowance for seeder priming and overflow	Exact quantity only	Seed runs out before paddock complete	Add 3-5% to calculated total for priming, calibration runs and end-of-paddock overflow.