Garden / Crops
Seed Rate Calculator: kg/ha from Thousand-Seed Weight
Calculate a seeding rate for cereals, oilseeds, and other crops: enter the plants you want per square metre or square foot, the thousand-seed weight of your seed lot, its germination, and the expected field survival, and get the rate per hectare or acre, the seed for the whole field, and the seeds to sow.
Seed Rate Calculator: kg/ha from Thousand-Seed Weight: Seed rate in kg/ha is the target plants per m² times the thousand-seed weight in grams, divided by establishment in per cent. For 250 wheat plants per m², a thousand-seed weight of 45 g, and 80% establishment, that is 250 × 45 ÷ 80 = 140.6 kg/ha, from 312 seeds sown per m². Runs 100% locally in your browser with zero server file uploads.
- Category
- Home & family tools
- Runs
- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Runs entirely in your browser
Seed rate = target plants per m² × thousand-seed weight in grams ÷ establishment in per cent, the formula used by AHDB in the UK. Establishment is germination times the share that survives in the field, often 70 to 90% for cereals, lower in cloddy, cold, or late-sown seedbeds. Weigh 1,000 seeds from your own seed lot, or use the weight on the certificate, since it varies widely between varieties and years.
Measure thousand kernel weight (TKW)
Thousand kernel weight (TKW), also called thousand-grain weight or thousand-seed weight, is the mass in grams of 1,000 seeds. Count 1,000 seeds from a representative sample of the seed lot, tare the weighing container, and weigh the seeds. For a smaller counted sample, TKW (g) = sample weight (g) × 1,000 ÷ seed count. The sample helper calculates this value and uses it in the seed rate.
For example, 200 seeds weighing 9 g have a TKW of 9 × 1,000 ÷ 200 = 45 g; weighing 1,000 of the same seeds would give about 45 g. Repeat with another representative sample to check your estimate. The Western Australian wheat sowing guide (https://www.agric.wa.gov.au/sites/gateway/files/2018%20Wheat%20Variety%20Sowing%20Guide%20for%20Western%20Australia.pdf) describes counting and weighing 1,000 seeds to measure seed weight.
Formula
Seed rate (kg/ha) = target plants per m² × TKW (g) ÷ expected establishment (%). In this calculator, establishment (%) = germination (%) × field survival (%) ÷ 100. For 250 plants/m², TKW 45 g, germination 100%, and field survival 80%, the rate is 250 × 45 ÷ 80 = 140.625 kg/ha, or 140.6 kg/ha rounded; 10 ha needs 1,406.25 kg. At the same plant target and establishment, heavier seeds need more kg/ha. AHDB's wheat trial protocol (https://rl.ahdb.org.uk/media/5728/protocol-002-early22-26-ahdb-rl-early-sown-wheat-trial-protocol-h22-26-jan-2022.pdf) gives the formula with germination and establishment as separate factors.
Spacing in a garden bed
For vegetables and flowers in beds, use the plant spacing calculator.
How to use it
- Enter the target plants per m² or ft².
- Enter the thousand-seed weight, germination, and field survival.
- Read the seed rate and the total for your area.
Privacy & limitations
Everything is calculated in your browser.
Related tools
Frequently asked questions
How do I calculate thousand kernel weight?
Count 1,000 seeds from a representative sample of your seed lot and weigh them in grams; that weight is the thousand kernel weight (TKW), also called thousand-seed weight. For N counted seeds, TKW (g) = sample weight (g) × 1,000 ÷ N. For example, 200 seeds weighing 9 g give a TKW of 45 g. Select the sample helper to calculate it and use it in the seed rate.
What is thousand-seed weight?
The weight in grams of 1,000 seeds; it varies between varieties and seed lots, so a fixed kg/ha can mean very different plant numbers.
What establishment should I expect?
Often 70 to 90% for cereals in a good seedbed, less when sowing late, into cold or cloddy soil, or after slug damage.
Where do I find the germination figure?
On the seed certificate or bag label; for home-saved seed, test a sample of 100 seeds on damp paper.
Free tool · runs in your browser · no account required