Seeding Rate Calculator
Work out how much seed to order or cart for a paddock. Enter a seeding rate and area for a straight kilograms-and-tonnes total, or switch to target-plant mode — give a target plant population, thousand-grain weight, germination and establishment — and it back-calculates the kg/ha rate you should drill.
Enter Values
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How to use this calculator
- For a simple total, enter your seeding rate (kg/ha) and the area (ha).
- To derive a rate, leave the rate blank and enter target plants/m² and thousand-grain weight (g), plus germination % (default 90) and establishment % (default 100).
- Read the calculated rate (target mode) and the total seed in kilograms and tonnes.
How it works
Total seed = seeding rate × area, converted to tonnes by dividing by 1,000. In target-plant mode the rate is built up from the agronomy: seeds per hectare = target plants/m² × 10,000; the base rate (kg/ha) = seeds/ha × TGW in grams ÷ 1,000,000; then that base is divided by germination% × establishment% to cover seeds that fail to germinate and seedlings that fail to establish. If you don't enter your own rate, this calculated rate is used for the total.
Worked example
Worked example. 80 kg/ha over 120 ha = 9,600 kg = 9.6 t. Target mode: 150 plants/m², TGW 45 g, 90% germination, 85% establishment → seeds/ha = 1,500,000; base = 1,500,000 × 45 ÷ 1,000,000 = 67.5 kg/ha; adjusted = 67.5 ÷ (0.90 × 0.85) = 88.24 kg/ha.
Common mistakes
- Using bag germination on old or poorly stored seed — retest, because a lower germination % lifts the required rate.
- Forgetting establishment losses (frost, insects, crusting), so the target plant count isn't actually reached in the field.
- Entering thousand-grain weight in the wrong units — TGW is the weight of 1,000 seeds in grams, not per seed or per 100.
Frequently asked questions
What is thousand-grain weight (TGW)?
It's the weight in grams of 1,000 seeds — a measure of seed size that varies by crop, variety and season. Bigger, heavier seed (higher TGW) needs more kilograms per hectare to hit the same plant population, which is why it drives the rate calculation.
What's the difference between germination and establishment?
Germination % is the share of seeds that sprout under ideal conditions (from a seed test). Establishment % is the share of germinated seedlings that actually survive to become plants in the paddock. Dividing by both converts a target plant count into the extra seed you must sow to allow for each loss.
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Tip: Enter any known values to calculate the remaining results.
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