How to use the pure live seed calculator
- Enter the purity and the germination from the seed tag, and the hard or dormant seed if you count it.
- Enter the pure live seed rate you want to sow, the area and the price per bulk pound or kilogram.
- Pick pounds and acres or kilograms and hectares.
- Read the pure live seed percent, the bulk seed rate and amount, and the cost per pound or kilogram of pure live seed.
Formula
Pure live seed fraction = purity x (germination + dormant seed counted)
Bulk seed rate = wanted pure live seed rate / pure live seed fraction
Bulk seed for the area = bulk rate x area
Cost per pure live seed unit = bulk price / pure live seed fraction
Purity is the share of the bag that is the wanted seed and germination is the share of that seed that will sprout. Together they say how much of the bag is live seed.
A lot that is 95 percent pure and 85 percent germinating
With 95 percent purity, 85 percent germination and 5 percent hard seed counted, the lot is 85.5 percent pure live seed. To sow 20 pounds of pure live seed per acre needs 23.392 pounds of bulk seed per acre, or 233.92 pounds for 10 acres. At $2.50 a bulk pound, the bulk seed costs $584.80, and each pound of pure live seed costs $2.92.
A metric lot at 98 percent purity and 90 percent germination is 88.2 percent pure live seed, so 15 kilograms of pure live seed per hectare needs 17.007 kilograms of bulk seed per hectare.
Why compare by pure live seed
Two bags with the same price can hold very different amounts of live seed. The cost per pound of pure live seed puts lots with different tags on the same footing, so a cheaper bag with low germination does not look better than it is. It also shows how much extra bulk seed to buy to reach the planting rate.
If you plan by plants instead of seed weight, the seed quantity calculator and the plant spacing calculator help. For lawns see the grass seed calculator, and for the soil itself the soil texture calculator.
Dormant and hard seed
Some seed is alive but has not sprouted at the time of the test, because of a hard coat or dormancy. Some programs count it toward pure live seed and some do not. The page lets you enter the percent you want counted, and 0 leaves it out.
Assumptions and limits
- Purity, germination and any dormant seed are taken from the seed tag and are for the lot you hold.
- The wanted rate is a pure live seed rate from your own plan, not a recommendation from this page.
- Germination plus dormant seed counted cannot be more than 100 percent.
- Prices are the ones you enter and no tax, delivery or coating weight is added.
Frequently asked questions
What is pure live seed?
It is the share of a seed lot that is both the wanted seed and alive. It equals purity times germination, with dormant seed added if it is counted.
How do I calculate the bulk seed needed?
Divide the pure live seed rate you want by the pure live seed fraction. At 85.5 percent, 20 pounds of pure live seed needs 23.39 pounds of bulk seed.
Why compare cost per pound of pure live seed?
Bags differ in purity and germination, so the bag price alone can mislead. Dividing by the live fraction shows what you pay for each pound that will grow.
Does the tag date matter?
Yes. Germination changes as seed ages, and tags show the test date. Use the figures for the lot you are actually buying.