How Much Seed Is Required per Acre? Seed Rate Explained Simply

"How much seed per acre?" sounds like it should have one answer. Crop guides give a figure – or more often a range, like "8–10 kg per acre". But two farmers sowing the same crop can need quite different amounts, and both be right. The difference comes down to the seed itself.

Seed rate depends on four things

1. How many plants you want – decided by spacing or a target population.
2. How heavy each seed is – measured as the 1000-seed weight, or test weight.
3. How many seeds will germinate – the germination percentage.
4. How clean the seed lot is – physical purity, meaning how much of the lot is actually seed of your crop rather than broken seed, weed seed or dirt.

Change any of these and the kilograms you need change too.

The seed rate formula

Seeds needed = Plants wanted × Seeds per hill ÷ (Germination % × Purity %)
Seed weight (kg) = Seeds needed × 1000-seed weight (g) ÷ 1,000,000

The division by germination and purity is what makes up for seeds that won't produce a plant.

Example: hybrid maize

Spacing 60 × 20 cm, 1 seed per hill, test weight 280 g, germination 90%, purity 98%:

• Plants per acre = 4,046.86 ÷ (0.60 × 0.20) = 33,724
• Seeds needed = 33,724 ÷ (0.90 × 0.98) = 38,236
• Seed weight = 38,236 × 280 ÷ 1,000,000 = 10.7 kg per acre

With a bolder hybrid at 350 g test weight, the same stand needs 13.4 kg. With 75% germination instead of 90%, it rises to 12.8 kg. That's why a single "correct" seed rate doesn't exist.

What is test weight and how do I find it?

Test weight is simply the weight of 1,000 seeds in grams. It's often printed on certified seed packets. If not:

1. Count 100 seeds at random from the bag.
2. Weigh them on an accurate scale.
3. Multiply by 10.

Do it two or three times and average. Rough ranges: wheat 35–50 g, paddy 20–30 g, maize 200–350 g, soybean 100–150 g, mustard 3–6 g.

Why a germination test is worth the effort

Germination on the packet is a minimum at the time of testing. Seed stored through a hot, humid summer – especially farm-saved seed – can lose viability. A home test takes a week and costs a handful of seeds: put 100 seeds on a wet cloth, roll it up, keep it moist and count the healthy sprouts after 5–7 days.

The Germination Percentage Calculator converts your count into a percentage and adjusts the recommended seed rate to match.

What about broadcast and drilled crops like wheat?

Wheat and other closely sown crops don't have a clear plant-to-plant spacing, so seed rate recommendations are usually given directly in kg per acre. You can still use the same logic to adjust them: if the recommended rate assumes 85% germination and your seed tests at 75%, increase the rate by 85 ÷ 75 = 1.13, i.e. 13%. Bold-seeded varieties may also need a higher rate by weight.

Don't forget losses in the field

A seed that germinates in a wet cloth may still fail in a cloddy, dry or crusted seedbed, or be eaten by birds and soil insects. Many farmers add 5–10% for field losses in difficult conditions. Good seedbed preparation and seed treatment reduce the need for this margin – see the Seed Treatment Calculator for working out treatment chemicals.

Quick checklist before you buy seed

• Decide your spacing or target population.
• Note the test weight, germination and purity on the packet – or measure them.
• Calculate with the Seed Rate Calculator.
• Add a small margin for gap filling and field losses.