In short
Thousand seed weight is the weight in grams of 1,000 seeds, measured by counting a sample of pure seed and weighing it.
It is a measure of seed size that varies between crops, varieties, years and fields, and it feeds straight into seed rate, because drills are set by weight while guides give seed counts. Winter wheat sits at 46 to 56 g in Irish variety tables, canola at 2.5 to 5.5 g and flax at 5 to 6.5 g in Alberta tables. In Planva, thousand seed weight is a field in the seed catalogue, next to germination and purity.
What thousand seed weight tells you
Alberta Agriculture defines it as the weight in grams of 1,000 seeds and calls it a measure of seed size. Seed size can differ from one crop to another, between varieties of the same crop, and from year to year or field to field. Because of that, the number of seeds in a kilogram of seed is highly variable. Thousand seed weight is how you correct for it.
How to measure it
The International Seed Testing Association treats two counting methods as equivalent. One counts and weighs the whole pure seed fraction of the purity working sample. The other takes 8 groups of 100 pure seeds and counts them by hand. Alberta gives the simplest farm version. Count out 1,000 seeds and weigh them in grams.
- Take pure seed. Remove chaff, broken kernels and weed seed first, because the figure describes the crop seed only.
- Count without choosing. Do not pick the biggest or best-looking seeds.
- Weigh on scales that read to 0.01 g. Weigh each group of 100 on its own.
- Scale up. The weight of eight groups of 100 multiplied by 1.25 gives the weight of 1,000. If one group is far from the rest, recount it.
- Repeat for every lot. A new lot is a new measurement.
Typical values
| Crop | Thousand seed weight, g | Where the figure comes from |
|---|---|---|
| Winter wheat | 46 to 56 | Teagasc, Irish winter wheat variety tables |
| Winter barley | 45 to 60 | Teagasc, Irish variety tables |
| Winter oats | 35 to 49 | Teagasc, Irish variety tables |
| Canola, Argentine type | 2.5 to 5.5 | Alberta Agriculture: 2.5 to 4 open-pollinated, 3 to 4.5 synthetic, 3.5 to 5.5 hybrid |
| Canola, Polish type | 2 to 3 | Alberta Agriculture |
| Flax | 5 to 6.5 | Alberta Agriculture |
These are regional and variety-based figures, not world averages. Alberta uses 35 g for wheat in its own worked example, 11 g below the lower end of the Irish range for winter wheat, which shows how far the same crop can differ between places.
Why a catalogue figure is not enough
- List values are averages. Teagasc points out that the thousand grain weight printed on a recommended list is the three-year average, not the figure for the crop in your barn.
- Size moves with the season. Dry or cool years change grain fill, and so the weight of the same variety.
- Weight changes the sum. At 4.5 million seeds per hectare, grain of 45 g needs about 203 kg/ha before corrections and grain of 40 g needs 180 kg/ha.
Using the figure
Seeds per kilogram = 1,000,000 ÷ thousand seed weight in grams. Grain of 35 g gives about 28,600 seeds per kilogram, and grain of 55 g about 18,200. The seed rate guide shows where the figure enters the kg/ha formula, and wheat seeding rate works through seeds per square metre.
How this works in Planva
- Seed catalogue. Thousand seed weight is held next to reproduction, germination, maturity group, purity and tillering.
- Agroplan. Seed is entered by rate or quantity, planned and actual.
Sources
Common questions
It is the weight in grams of 1,000 seeds of a crop, measured on pure seed. It describes seed size and is also called thousand kernel weight or thousand grain weight.
The real Planva interface, shown with test data.
