Agrimetra

Seeding rate calculator

Soybeans with a thousand-seed weight of 150 g, a target stand of 35 plants per m² and 90 % germination against 8 % field losses need 56.6 lb of seed per acre — the same rate written the other way is 63.4 kg/ha, or 42 seeds drilled per square metre, because only 82.8 % of what the drill puts down is expected to stand up as a plant. Type the two figures from your own seed label and the rate follows them, and the job sheet turns it into seed for the whole field, whole bags and what is left in the last one.

The answer updates as you type — there is no button to press.

No fields saved yet — measure one and save it below.

ac

e.g. 80 ac — for the whole-field totals on the job sheet.

g

On the seed label — e.g. 45 g for wheat.

e.g. 350 for winter wheat, 9 for maize.

%

From the seed label — e.g. 92 %.

%

Leave empty for 100 %.

%

What you expect not to come up — e.g. 10 %.

kg

For the last-bag line — e.g. 25 kg or a 500 kg big bag.

Optional — for the cost line.

Your answer

Seeding rate169.7 lb/ac

The same rate the other way
190.2 kg/ha
Seeds to drill per m²
423
Seeds that should become plants
82.8 %

Field job sheet

Type the field area above (or pick a saved field) to get the whole-field total, the last bag and a sheet to print or send.

How the answer is worked out

A seeding rate is one division carried through three corrections, and every term in it is on the bag in front of you:

  1. Seeds you want to stand — the target plant population, in plants per square metre.
  2. Seeds you have to drill — the target divided by germination, then divided again by purity and by what you expect not to come up in the field. A target of 35 plants at 90 % germination and 8 % field losses means drilling about 42 seeds per square metre.
  3. Weight of that many seeds — seeds per square metre multiplied by the thousand-seed weight, divided by 1,000, gives grams per square metre, and ten grams per square metre is a hundred kilograms per hectare.

The imperial rate is the same number converted once at the end: 1 kg/ha is 0.8922 lb/ac, so nothing is rounded twice.

The crop picker only saves typing

Choosing a crop fills the thousand-seed weight and the target stand with a common value for it and then gets out of the way — every figure stays editable, and the rate is computed from what is actually in the boxes. That matters because thousand-seed weight is a property of the lot, not of the crop: two bags of the same wheat variety in the same shed can be 42 g and 51 g, and a rate worked out from a published table is wrong for both. This page therefore prints the value used for your case, never a table of crop figures to copy from.

Field losses are a judgement, not a constant

The one term nobody can read off a label is what the field will take. A fine, firm, moist seedbed drilled on time loses a few per cent; a late, cloddy or cold one can lose a quarter of the stand. Put in what your own fields have done in the last few seasons and keep the assumption visible — it is the difference between a rate that holds and one that has to be fixed with a re-drill.

A worked example

Every figure below is computed by the calculator above from this case — nothing here is typed in by hand:

Crop
Soybean
Thousand-grain weight
150
Target plants per m²
35
Germination
90
Field losses
8

Seeding rate:56.6 lb/ac

The same rate the other way
63.4 kg/ha
Seeds to drill per m²
42
Seeds that should become plants
82.8 %

Worked by Agrimetra with the same engine the calculator above runs.

What this means in the United States

US row crops are ordered in seeds per acre — corn and soybeans are sold by the unit of seeds, not by weight — while small grains are still drilled by the pound. The calculator carries both, because a seed order and a drill setting are the same decision in two units.

Questions growers actually ask

Why does the rate change when I type a different thousand-seed weight?
Because the drill meters seeds and the bag is sold by weight. The number of seeds you want per square metre is fixed by the target stand; the weight that carries them is the thousand-seed weight, so a lot at 150 g and a lot at 170 g of the same crop are two different rates for the same field.
What is the difference between germination and field losses?
Germination is measured in a laboratory and printed on the seed label. Field losses are what the seedbed, the drilling depth, the slugs and the weather take on top of it. The calculator applies both, and the line "seeds that should become plants" is the two of them multiplied together — 82.8 % in the example above.
Do I have to fill in purity?
No. Leave it empty and the calculator treats the lot as 100 % pure, which is close enough for certified seed. Grass and clover lots are where purity is worth typing, because chaff and inert matter can be several per cent of the bag weight.
Can I get the answer in seeds per acre instead?
Corn and soybeans are ordered in units of seeds rather than by weight, so the page prints seeds per square metre alongside the weight rate, and the planting population calculator takes the same field from the other end — row spacing and seed spacing into plants per acre.

Last updated:

Sources

Calculators that use the same field