Thousand-grain weight
The weight in grams of 1,000 seeds from one seed lot.
It tells you how big the seeds are. Bigger seeds mean fewer seeds in every kilogram, so you need more kilograms to sow the same number of plants.
Illustration, not to scale
Why it matters
You sow plants, not kilograms.
A crop needs a certain number of plants per square metre. Seed is sold and metered by weight. TGW is the bridge between the two, and it changes from lot to lot and year to year.
How to find it
Read the label, or count and weigh.
- Check the seed label or certificate first.
- If it is not there, count out 100 seeds.
- Weigh them in grams on a fine scale.
- Multiply by 10. Repeat a few times and average.
Where it is used
TGW in the seed rate formula.
The formula
seed rate (kg/ha) =
target plants per m² × TGW ÷ 100
÷ (germination % × field emergence %)
Germination comes from the seed label. Field emergence is your estimate of how many viable seeds become plants in your conditions.
Open the full seed rate calculatorThat is 24 kg/ha more than the same plant count with 40 g seed.
Starting values are an example for a small-grain cereal, not a recommendation.
Typical TGW, small grains
Typical rangeCommon mistakes
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Reusing last year's figure. TGW changes with variety, season and seed lot.
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Sowing a fixed kg/ha every year. The same weight of larger seed gives fewer plants.
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Confusing it with bulk density. Hectolitre or bushel weight measures a volume of grain, not seed size.
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Weighing one small sample. Count and weigh several samples and average them.
About this page
Reference information, not professional advice. Conditions vary by field.
FAQ
Frequently asked questions
- TGW stands for Thousand-Grain Weight — the mass in grams of exactly 1,000 seeds of a given crop lot. It is sometimes called thousand-seed weight (TSW).
- Seed rate is calculated by target plant population × TGW ÷ germination % ÷ field emergence %. If you use the wrong TGW you will over- or under-sow, potentially reducing yield or wasting expensive seed.
- Count out four replicates of 100 seeds each, weigh each sample to 0.01 g precision, multiply each weight by 10 to convert to the 1,000-seed equivalent, then average the four results. Discard any replicate that differs from the mean by more than 5 %.
- Wheat TGW commonly falls between 35 g and 55 g, but this varies by variety, season and growing conditions. Always use the figure from your own seed lot label or your own measurement rather than a textbook average.
- Yes. TGW is influenced by the weather during grain fill, harvest timing, post-harvest drying temperature and storage conditions. Even the same variety can vary by 10–15 % between seasons.
- No. Bulk density (hectolitre or bushel weight) measures how much a given volume of grain weighs — it depends partly on how grains pack together. TGW measures individual seed mass directly and is the relevant figure for seed rate calculations.
- Certified seed labels in most countries must show germination percentage and variety name; TGW is often included as additional information. If it is absent, ask your seed merchant for the lot-specific technical data sheet or measure it yourself.