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Seed Calculators

Seed Rate Calculator

Calculate how many kilograms of seed you need per acre from spacing, 1000-seed weight, germination and purity.

Enter your details

Seeds dropped at each spot.

Weight of 1,000 seeds in grams. Often printed on the seed packet.

g
%

Share of the lot that is pure seed of the crop.

%

Please note: This calculator provides a mathematical estimate based on the values entered. Recommended agricultural application rates can vary by crop, soil, product formulation, location and official agricultural guidance. Check the product label and local agricultural recommendations before application.

How much seed should you buy? It depends on four things: how far apart you sow, how heavy each seed is, how many of them will actually germinate, and how clean the seed lot is. Enter them below to get the seed rate in kg per acre and the total for your field.

About the Seed Rate Calculator

Seed rate tables in crop guides give a range – "8 to 10 kg per acre" – because the right figure depends on the seed lot in your hands. A bold-seeded variety weighs more per thousand seeds. A lot with 75% germination needs more seed than one with 95%. This calculator uses the actual numbers for your seed and your spacing, so you buy what you need and get the stand you planned.

It works in three stages:

  1. How many hills? The field area divided by the space each hill occupies (row spacing × plant spacing).
  2. How many seeds? Hills × seeds per hill, then increased to allow for seeds that won't germinate and for impurities in the lot.
  3. How many kilograms? Seeds × 1000-seed weight.

It suits crops sown at a definite spacing – maize, cotton, sunflower, soybean, pigeon pea, vegetables and dibbled or line-sown crops. For crops that are broadcast or drilled continuously, such as wheat, use the plant spacing that gives your target number of plants per square metre, or follow the recommended seed rate and adjust it with the Germination Percentage Calculator.

How to use the Seed Rate Calculator

  1. 1 Enter the area you are sowing.
  2. 2 Enter row-to-row and plant-to-plant spacing. You can use centimetres, metres, inches or feet.
  3. 3 Enter the seeds you drop per hill – 1 for most hybrids, 2 or 3 if you plan to thin later.
  4. 4 Enter the 1000-seed weight (test weight) from the packet, or weigh 100 seeds and multiply by 10.
  5. 5 Enter the germination % (from the packet or your own test) and purity %, then press Calculate.

The formula we use

Hills = Area (m²) ÷ (Row spacing (m) × Plant spacing (m))
Seeds to sow = Hills × Seeds per hill ÷ (Germination % × Purity %)
Seed rate (kg) = Seeds to sow × 1000-seed weight (g) ÷ 1,000 ÷ 1,000

This is the standard seed-rate formula used in agronomy textbooks. Some versions also include a "field emergence" factor for losses after germination – if you want to allow for that, simply lower the germination percentage.

Worked example

Hybrid maize on 1 acre at 60 × 20 cm, 1 seed per hill. The packet says test weight 280 g, germination 90%, purity 98%.

  1. Space per hill = 0.60 × 0.20 = 0.12 m².
  2. Hills = 4,046.86 m² ÷ 0.12 = 33,724.
  3. Seeds to sow = 33,724 ÷ (0.90 × 0.98) = 38,236.
  4. Seed = 38,236 × 280 g ÷ 1,000 ÷ 1,000 = 10.71 kg per acre.

Maize seed is sold in 4 kg or 5 kg packs, so you would buy 12 kg for this acre and keep a little for gap filling.

Things to keep in mind

  • Test your own seed. The germination on the packet is the minimum at the time of testing. Storage in heat and humidity reduces it. A quick home test takes 5–7 days.
  • Field conditions matter. Poor seedbed, crusting, low soil moisture or pest damage all reduce emergence. Many farmers add 5–10% to the calculated rate in difficult conditions.
  • Follow crop-specific advice. Recommended plant populations differ by crop, variety, season and irrigation. Use the spacing advised for your situation.
  • Treat your seed. If the recommendation calls for seed treatment, work out the chemical with the Seed Treatment Calculator.

Frequently asked questions

What is the formula for seed rate?

Seed rate (kg/ha) = (number of plants per ha × seeds per hill × 1000-seed weight in g) ÷ (germination % × purity % × 10,000), with germination and purity entered as percentages. The calculator above applies this formula for any area and spacing.

What is test weight?

Test weight is the weight of 1,000 seeds in grams. It tells you how big and bold the seed is. It is essential for converting a number of seeds into kilograms.

How do I measure test weight at home?

Count 100 seeds at random, weigh them on an accurate kitchen or jeweller's scale, and multiply by 10. Repeat two or three times and average for a better figure.

Why does low germination increase seed rate so much?

Because you have to sow extra seeds to make up for those that fail. At 60% germination you need 1.5 times as many seeds as at 90%.

Can I use this for paddy nursery?

For transplanted paddy, the seed rate depends on the number of seedlings per hill and hills per square metre in the main field. Enter the transplanting spacing and seedlings per hill as "seeds per hill", and add a margin because not every nursery seedling is used.

Does it work for vegetables?

Yes. For small-seeded vegetables the test weight is only a few grams, so the result may be in grams – for example 0.15 kg means 150 g.

Guides that use this calculator

Last updated . Spotted a mistake or need a unit we don't support? Tell us.