Free calculator
How much fertilizer should you apply?
Pick a target nitrogen rate, enter the N-P-K label, and see the product weight and bags needed for your lawn.
Product estimate
Product needed
15.6lb
Bags to buy
1× 50 lb
N applied
3.75lb
Whole-bag N
12lb
Whole-bag N rate
2.4lb / 1,000
Phosphate applied
0lb
Potash applied
0.94lb
The formula
Product weight = (area ÷ 1,000 × target lb N per 1,000 sq ft) ÷ (N % ÷ 100). Phosphate and potash are then calculated from the same product weight and their label percentages.
The whole-bag line matters. You may need 18.2 lb of product but only be able to buy 25 lb bags. Applying the whole bag would put down more nitrogen than planned, so the calculator shows that number separately.
Before you apply
Check the label for the maximum annual nitrogen rate, the application timing, and any restrictions. A soil test is the right way to decide whether phosphorus or potassium is needed at all. Do not add nutrients just because a bag contains them.
Sweep granules off pavement and keep them away from storm drains, wells, and waterways. Local rules can be stricter than the label.
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