FREE LAWN SEED QUANTITY TOOL · METRIC
Grass Seed Calculator & Bag Estimator
Measure the lawn, enter the seeding rate printed for your grass-seed product and calculate the kilograms and whole bags to buy. Add an allowance and bag price only when they are useful to your real project.
GRASS SEED QUANTITY CALCULATOR
Turn your lawn area and the bag label rate into seed weight and bags.
Measure the area, enter the seeding rate printed for your product and project type, then add an optional allowance and bag size. Tiny Mustard Seed does not invent a universal grass-seed rate.
FORMULA
seed kg = lawn area (m²) × label rate (g/m²) ÷ 1,000 · purchase kg = seed kg × allowance · bags = purchase kg ÷ bag size, rounded upUse the product label rate for the job you are doing.New-lawn seeding and overseeding can use different rates, and grass mixtures vary. Enter the rate printed for your specific seed rather than relying on a generic preset.
Area × label rate gives the base seed weight.
The useful calculation is straightforward once the lawn area and the correct product rate are known. A label rate expressed in grams per square metre is multiplied by the lawn area, then divided by 1,000 to convert grams to kilograms. For example, 50 m² at 35 g/m² requires 1.75 kg before any extra allowance.
If the bag expresses its rate as kilograms per 100 m², Tiny Mustard Seed converts that rate first. A rate of 3.5 kg/100 m² is the same as 35 g/m². Keeping both input formats available avoids forcing you to manually convert the supplier's label before using the calculator.
Choose the correct rate before you calculate.
Grass-seed products can give different application rates for establishing a new lawn and for overseeding an existing lawn. The correct rate can also vary by grass mixture, seed size, intended use and manufacturer. That is why this calculator deliberately does not apply a hidden “new lawn” or “overseeding” multiplier.
Read the product label and enter the rate that matches your project. If the bag provides a range, choose the rate that fits the supplier's instructions and the real site conditions rather than assuming the highest number is automatically better. The calculator's job is quantity arithmetic; the seed producer's label remains the more specific source for how that product should be applied.
Use the area that will actually receive seed.
For a simple rectangular lawn, multiply length by width. The calculator can do that directly. If you already know the total area, switch to known-area mode and enter the square metres instead. For an irregular lawn, divide the site into simpler shapes, calculate their areas separately and add them before entering the total.
Exclude patios, paths, sheds, permanent beds and other surfaces that will not be seeded. Small measuring errors can become meaningful on a large lawn, especially when the seeding rate is high. If you are unsure of the footprint, the separate Garden Area Calculator can help with rectangular, circular and triangular sections before you return here for the seed quantity.
Keep the mathematical requirement separate from the purchase quantity.
The base quantity is the lawn area multiplied by the label rate. The optional allowance is applied after that base quantity so you can see what extra seed you are choosing to include. An allowance may be useful for small measuring errors, uneven hand spreading or keeping a modest reserve for later patching. It is not a recommendation to deliberately exceed the product's application rate across the lawn.
Bag quantity is a purchasing calculation. Tiny Mustard Seed divides the allowed seed weight by the bag size and rounds upward to the next whole bag. The leftover result shows how much seed remains beyond the calculated project quantity after that rounding. Keep any unused seed according to the storage instructions on the package.
Compare package sizes using the rounded bag count.
If you enter the price of one bag, the calculator multiplies that price by the number of whole bags required. This is useful when comparing two package sizes: change the bag size and price and look at both the total cost and the amount left after the calculated project quantity.
A cheaper price per kilogram is not always the cheapest project purchase if it forces you to buy much more seed than needed. The calculator keeps the seed requirement, whole-bag purchase and leftover quantity visible together so the trade-off is easier to see.
Seed quantity is only one part of establishing a lawn.
The calculator does not assess soil preparation, seed-to-soil contact, watering frequency, germination temperature, shade tolerance, drainage, mowing or whether a particular grass mixture fits your climate. Those decisions can affect establishment far more than small differences in arithmetic.
Follow the seed label for application and establishment guidance, and adjust the wider plan to the real garden. If you need to estimate irrigation volume for a measured lawn area, use the Rain-Adjusted Garden Watering Calculator separately rather than turning the grass-seed rate into a water recommendation.
Should I use a new-lawn rate or an overseeding rate?
Use the rate printed by the seed manufacturer for the job you are actually doing. New lawn establishment and overseeding can use different rates, and different grass mixtures can also specify different quantities.
Why does the calculator ask for the product label rate?
There is no single seed rate that fits every grass mixture, seed size, establishment method or product. Using the label rate keeps the calculation tied to the seed you are buying instead of hiding a generic assumption.
What does the extra allowance do?
The allowance adds a percentage after the base seed weight is calculated. It can cover small measurement errors, uneven spreading or a little reserve seed. Set it to zero when you want the pure label-rate quantity.
Why are bags rounded up?
Retail seed is normally bought in whole bags or boxes. If the calculated purchase quantity is larger than an exact number of bags, the next whole bag is required to meet the entered target.
Can I enter kg per 100 square metres instead of grams per square metre?
Yes. The calculator accepts either g/m² or kg/100 m² and converts both to the same internal rate before calculating the seed weight.