Enter the plant stand you are aiming for, the thousand-seed weight of your lot and the germination and purity from the seed label. You get the seeding rate in kg/ha, the seed needed for your plot, and — if you add a row spacing — the seed spacing to set on the planter. Everything is computed in your browser.
The stand you want after emergence.
Printed on the seed bag — it differs between lots.
From the seed label.
Share of the bag that is seed of this crop.
Add it to get seeds per metre of row and the seed spacing for the planter.
Enter the target density, thousand-seed weight, germination and purity.
How it works
The chain has two steps. First, not every seed becomes a plant: dividing the target density by germination × purity gives the number of seeds that must be sown. Second, mass follows from the thousand-seed weight, since seeds/ha × TKW in grams ÷ 1,000,000 is the rate in kg/ha. Both label figures matter — 90% germination instead of 98% raises the seed quantity by almost 9%.
Thousand-seed weight (masa 1000 zrna) varies between lots of the same variety, sometimes by a fifth, which is why the bag states it. Using a catalogue average instead of the figure on your bag is the most common source of a wrong rate. Density can be entered per hectare, which suits maize and sunflower, or per square metre, which is how cereal stands are usually specified — 550 plants/m² is 5,500,000 per hectare.
Add a row spacing and the tool converts the rate into planter geometry: metres of row per hectare (10,000 ÷ row spacing in metres), seeds per metre of row, and the distance between seeds inside the row. That last number is what you actually dial into a precision planter or check by counting seeds along a measured metre after the first pass.
Practical examples
Maize at 70,000 plants per hectare
With TKW 300 g, germination 95% and purity 99%, you need 74,429 seeds/ha and 22.33 kg/ha. At 70 cm rows that is 5.21 seeds per metre of row, so about 19.2 cm between seeds.
Wheat at 550 plants per m²
A lot with TKW 42 g, 95% germination and 98% purity needs 5,907,626 seeds/ha, which comes to 248.12 kg/ha — 1,240.6 kg for a 5-hectare field.
Sunflower with heavy seed
Aiming for 60,000 plants/ha with TKW 65 g, 92% germination and 99% purity: 65,876 seeds/ha and only 4.28 kg/ha, because large seed still means few kilograms at low density.
A garden bed of 10 ari
10 ari is 0.1 ha, so a maize rate of 22.33 kg/ha becomes 2.23 kg of seed — the sort of quantity you buy in a bag rather than a pallet.
Frequently asked questions
What is thousand-seed weight and where do I find it?
It is the mass of 1,000 seeds in grams, printed on the seed bag or label because it changes from lot to lot. Larger, heavier seed means more kilograms for the same number of plants — for maize it is typically 250–350 g, for wheat 35–50 g.
Why divide by germination and purity?
Because you sow seeds, not plants. Germination is the share that will emerge under good conditions, purity the share of the bag that is actually seed of that crop. Multiplying them gives the usable fraction, and dividing the target by it tells you how many seeds to put in the ground.
Should I add anything for field losses?
Laboratory germination is measured under ideal conditions, so field emergence is usually a few percent lower. Many growers handle this by entering a germination figure a little below the label value, or by raising the target density slightly. The tool uses exactly what you type.
Can I enter the density per square metre?
Yes — switch the unit. Cereal recommendations are written per m² (450–650 plants for wheat), while maize and sunflower are quoted per hectare. One plant per m² equals 10,000 per hectare.
What is the seed spacing figure for?
It is the distance between seeds along the row, which is what a precision planter is set to. After the first pass you can verify it by digging along one metre of row and counting: at 19 cm spacing you should find about five seeds.
Does row spacing change the seeding rate?
No. The rate per hectare depends only on target density, TKW, germination and purity. Row spacing redistributes the same seed — wider rows mean more seeds per metre of row, narrower rows fewer.
Why is my maize rate only about 20 kg/ha when wheat needs 250?
Maize is planted at 60–80 thousand plants per hectare, wheat at 4–6 million. Even though maize seed is roughly seven times heavier, the hundredfold difference in plant count dominates.
Can I work backwards from a rate I already use?
Indirectly — adjust the target density until the kg/ha matches what you sow. That tells you the plant stand your habitual rate actually delivers with this lot, which is often the more interesting question.
Does it work for grass or a lawn?
Grass seed is sold by kg per 100 m² or per hectare rather than by plant count, so a rate is given to you directly. This tool is aimed at crops where you decide the plant stand.
How precise should the density target be?
Density recommendations come from your variety, soil moisture and sowing date, and are usually given as a range. The calculator is exact about arithmetic, not about agronomy — take the target from the seed company guidance or an agronomist.
Are units and decimal commas handled?
Yes. Areas can be square metres, ari or hectares, and both 6,5 and 6.5 are read as six and a half.
Is anything uploaded?
No. The calculation runs in your browser and nothing about your field or seed lot leaves the device.
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