Seed Rate Calculator — kg per Acre & Hectare from Spacing and Test Weight

Seed rate calculator with the standard formula

Sowing too little seed leaves gaps; sowing too much wastes money and makes plants compete. This seed rate calculator works out how many kilograms of seed you need per hectare, per acre and for your own field from the plant stand you want, the test weight (weight of 1,000 seeds), the germination and purity of your seed lot and, if you like, an allowance for poor field emergence.

You can start from row and plant spacing, from a target number of plants per square metre, or from a plant population per acre or hectare. The working is shown step by step, so you can check it against the formula in your agronomy notes. Fields can be in acres, hectares, bigha, guntha, cent or kanal.

How to use the seed rate calculator

1. Choose how you know the plant population: From spacing, Plants per m² or Plants per acre / ha.
2. Enter the spacing (or population). For hill sowing, set the number of seeds per hill.
3. Enter the test weight in grams per 1,000 seeds, and germination and purity from the seed bag or test report.
4. Lower field emergence below 100% if the seedbed is dry or cloddy, and add extra seed for gap filling if you wish.
5. Enter your field area and, optionally, the packet size to see how many packets to buy.

Seed Rate Calculator features

Seed rate formula

Seed rate (kg/ha) = plants per m² × test weight (g) ÷ 100 ÷ (germination × purity × field emergence), with the percentages written as fractions. From spacing, plants per m² = 10,000 ÷ (row spacing in cm × plant spacing in cm) × seeds per hill.

The “÷ 100” comes from the units: plants per m² × 10,000 m² per hectare × test weight ÷ 1,000 seeds ÷ 1,000 g per kg.

1. Moong at 30 × 10 cm: 10,000 ÷ 300 = 33.3 plants/m².
2. With a test weight of 36 g: 33.3 × 36 ÷ 100 = 12 kg/ha if every seed grew.
3. With 92% germination and 85% purity: 12 ÷ (0.92 × 0.85) = 15.3 kg/ha, or 6.2 kg per acre.

Seed rate for wheat — a worked example

Suppose the target is 250 plants per m², the seed lot weighs 40 g per 1,000 seeds, germination is 90%, purity 98% and you expect 90% of the germinating seeds to emerge. Then 250 × 40 ÷ 100 = 100 kg/ha, divided by 0.9 × 0.98 × 0.9 = 0.79 gives about 126 kg/ha (51 kg per acre) — close to the general wheat rate of 100–125 kg/ha.

Bold, heavy seed (a higher test weight) needs more kilograms for the same plant stand, which is why a fixed “kg per acre” from a neighbour can be wrong for your seed lot.

Getting the inputs right

• Test weight: count 1,000 seeds (or 4 × 100) and weigh them; many seed packets and test reports also print it.
• Germination: place 100 seeds on wet paper or in sand and count the seedlings after the period set for the crop; certified seed must meet minimum germination standards.
• Spacing: use your state package of practices — see the plant spacing calculator for plants per acre from any layout.
• Hybrid seed is sold by the packet and sown at lower rates; check the company’s recommendation.