OneTaskBy Tim King · Updated
Seeding Rate Calculator
Seed Rate From Target Plants and TSW
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How the Seeding Rate Calculator works
This seeding rate calculator turns a target plant population into a seed rate in kilograms per hectare and pounds per acre. It accounts for seed size, germination and field losses, so you drill enough seed to get the stand you want without wasting money.
How the seeding rate calculator works
Seed lots vary in size, so sowing by weight alone gives different plant numbers from one lot to the next. Thousand seed weight (TSW), printed on the seed label or found by weighing 1,000 seeds, fixes that. Not every seed germinates, and not every seedling survives frost, slugs and a rough seedbed, so the calculator scales up for both. The formula is seed rate (kg/ha) = target plants per m² × TSW ÷ (germination × establishment) ÷ 100, with germination and establishment as decimals.
First example. For 150 wheat plants per m² with a TSW of 40 g, 95% germination and 80% establishment, you need 197 seeds per m², or 78.9 kg/ha (70.4 lb/acre). A 20 ha field needs about 1,579 kg of seed.
Second example. Oilseed rape at 50 plants per m², TSW 5 g, 90% germination and 60% establishment needs 93 seeds per m², or just 4.6 kg/ha (4.1 lb/acre).
How many seeds per m² should I sow? It depends on the crop and timing. Winter wheat is often 200 to 350 seeds per m², spring barley 300 to 400 and oilseed rape 40 to 80.
Lower the establishment figure for late drilling, cloddy or dry seedbeds and high slug pressure. Your agronomist or seed merchant can give local targets.
Seed rate by target plant population and thousand-seed weight (95% germination, 80% establishment)
| Plants per m² | TSW 35 g | TSW 40 g | TSW 45 g | TSW 50 g | TSW 55 g |
|---|---|---|---|---|---|
| 150 | 69.1 kg/ha | 78.9 kg/ha | 88.8 kg/ha | 98.7 kg/ha | 108.6 kg/ha |
| 162.5 | 74.8 kg/ha | 85.5 kg/ha | 96.2 kg/ha | 106.9 kg/ha | 117.6 kg/ha |
| 175 | 80.6 kg/ha | 92.1 kg/ha | 103.6 kg/ha | 115.1 kg/ha | 126.6 kg/ha |
| 187.5 | 86.3 kg/ha | 98.7 kg/ha | 111.0 kg/ha | 123.4 kg/ha | 135.7 kg/ha |
| 200 | 92.1 kg/ha | 105.3 kg/ha | 118.4 kg/ha | 131.6 kg/ha | 144.7 kg/ha |
| 212.5 | 97.9 kg/ha | 111.8 kg/ha | 125.8 kg/ha | 139.8 kg/ha | 153.8 kg/ha |
| 225 | 103.6 kg/ha | 118.4 kg/ha | 133.2 kg/ha | 148.0 kg/ha | 162.8 kg/ha |
| 237.5 | 109.4 kg/ha | 125.0 kg/ha | 140.6 kg/ha | 156.3 kg/ha | 171.9 kg/ha |
| 250 | 115.1 kg/ha | 131.6 kg/ha | 148.0 kg/ha | 164.5 kg/ha | 180.9 kg/ha |
| 262.5 | 120.9 kg/ha | 138.2 kg/ha | 155.4 kg/ha | 172.7 kg/ha | 190.0 kg/ha |
| 275 | 126.6 kg/ha | 144.7 kg/ha | 162.8 kg/ha | 180.9 kg/ha | 199.0 kg/ha |
| 287.5 | 132.4 kg/ha | 151.3 kg/ha | 170.2 kg/ha | 189.1 kg/ha | 208.1 kg/ha |
| 300 | 138.2 kg/ha | 157.9 kg/ha | 177.6 kg/ha | 197.4 kg/ha | 217.1 kg/ha |
| 312.5 | 143.9 kg/ha | 164.5 kg/ha | 185.0 kg/ha | 205.6 kg/ha | 226.2 kg/ha |
| 325 | 149.7 kg/ha | 171.1 kg/ha | 192.4 kg/ha | 213.8 kg/ha | 235.2 kg/ha |
| 337.5 | 155.4 kg/ha | 177.6 kg/ha | 199.8 kg/ha | 222.0 kg/ha | 244.2 kg/ha |
| 350 | 161.2 kg/ha | 184.2 kg/ha | 207.2 kg/ha | 230.3 kg/ha | 253.3 kg/ha |
| 362.5 | 166.9 kg/ha | 190.8 kg/ha | 214.6 kg/ha | 238.5 kg/ha | 262.3 kg/ha |
| 375 | 172.7 kg/ha | 197.4 kg/ha | 222.0 kg/ha | 246.7 kg/ha | 271.4 kg/ha |
| 387.5 | 178.5 kg/ha | 203.9 kg/ha | 229.4 kg/ha | 254.9 kg/ha | 280.4 kg/ha |
| 400 | 184.2 kg/ha | 210.5 kg/ha | 236.8 kg/ha | 263.2 kg/ha | 289.5 kg/ha |
FAQ
What is thousand seed weight?
The weight in grams of 1,000 seeds. It varies with variety and growing season, so check the seed label or count and weigh a few hundred seeds yourself and scale up to 1,000.
What is the difference between germination and establishment?
Germination is the share of seeds that sprout in ideal lab conditions. Establishment is the share of seeds sown that become healthy plants in the field after soil, weather, pests and drill losses.
What establishment rate should I use?
Around 80 to 90% for an early sowing into a good seedbed, 70% for typical conditions and 50 to 60% for late sowing, heavy clay, dry soil or high slug pressure. Small seeds such as rape usually establish less well.
How do I convert kg/ha to lb/acre?
Multiply by 0.892. One kilogram per hectare equals 0.892 pounds per acre, so 100 kg/ha is about 89 lb/acre. The calculator shows both figures so you can set the drill in either unit.
Why do seed rates differ so much between crops?
Seed size varies enormously. A thousand beans can weigh 500 g, while a thousand rape seeds weigh 5 g, so the same plant count needs very different weights. Plant spacing targets also differ by crop.
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