Seeding Rate Calculator

How many kilos of seed per hectare you need to end up with the plants you want, allowing for what does not germinate and what germinates but never emerges.

Seeding rate

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Seeding rate—

Seed for the whole field—

Seeds you have to sow—

Seeds in total—

Of every hundred seeds, plants—

Cost per hectare—

Total seed cost—

How this was worked out

The formula

kg/ha = (target plants ÷ (germination × emergence)) × TKW ÷ 100

Where it comes from

A seeding rate is not decided in kilos: it is decided in plants per square metre, which is what drives the crop. From there you work up to weight, and two losses happen on the way. The first is germination, printed on the bag. The second is field emergence, which is always lower: of the seeds that germinate in a laboratory, some never make it through the seedbed. Thousand kernel weight is what turns a number of seeds into kilos, and it varies a lot between varieties of the same cereal: two wheats with the same plant target can need different rates purely because of grain size.

How to work it out by hand

Divide the plants you want by germination and by emergence, both as decimals
That gives the seeds you have to sow per square metre
Multiply by the thousand kernel weight in grams and divide by a hundred: those are the kilos per hectare
Multiply by the hectares to know how much seed to buy

What is worth knowing

Thousand kernel weight has to come with the lot, not be assumed: it is the figure that varies most and the one that throws the rate furthest off. And emergence is not a catalogue number but the one you get in that field with that seedbed: sowing late or into a poorly prepared soil drops it sharply, and that is where last year’s rate costs you.

Frequently asked questions

What is thousand kernel weight?

The weight in grams of a thousand seeds from the lot. It is what turns a number of seeds into kilos, and it comes on the label or from the supplier.

Why is emergence lower than germination?

Germination is measured in a laboratory under ideal conditions. In the field there is capping, drought, sowing depth and pests, so fewer come up.

Does it work for any crop?

Yes, as long as you know the plants per square metre you are after and the thousand kernel weight. The numbers change, the arithmetic does not.

What if I sow late?

You raise the rate, because emergence falls and the plant tillers less. The right way to do it is to lower the emergence figure, not to add kilos by eye.