Fertilizer Calculator
Convert area, target N, and a bag's N% into exactly how many pounds to apply.
Cool-season lawns: apply most N in fall. Vegetable beds: side-dress during the season per crop. Always follow the bag label and local fertilizer rules (some states restrict phosphorous).
What the inputs mean
Enter the area in square feet, the target amount of actual nitrogen you want per thousand square feet, and the N number printed on the bag. The tool divides out the concentration to give you the pounds of product rather than pounds of nutrient, which is the conversion most people get wrong.
How to act on the answer
Weigh or measure the product rather than estimating by eye, then apply it evenly — streaking a high-nitrogen product burns foliage while leaving most of the area underfed. After the first application, judge the result by growth rather than by schedule: too much nitrogen produces soft, sappy growth that invites sucking insects and delays fruiting, which is why the calculator asks for a target rather than a fixed rate.
What this tool cannot know
It cannot set the target for you, because the correct rate depends on a soil test, the crop, the organic matter already present, and what you applied last season. It also cannot tell you whether nitrogen is the limiting nutrient at all — adding nitrogen to a soil that is short on phosphorus or has a pH problem wastes the application. Test before you calculate.
Where it fits in the season
A calculator is only as good as the location data behind it, so two other pages usually belong in the same session. The ZIP lookup establishes your zone and typical frost dates, which is the baseline that fertilizer calculator is reasoning from, and the monthly zone checklists turn the same baseline into an ordered set of jobs for the current month. If you are working from a specific planting plan rather than a blank bed, the garden plan templates carry published spacing and crop lists you can feed straight into the planner.
Everything on this page runs in your browser from data shipped with the site. There is no account, nothing is uploaded, and the numbers you type are not stored on a server — which also means a printed sheet or a screenshot is the only copy you will have if you close the page. See all garden tools →
Related guides
Watering guide · Fertilizing guide · Composting guide · Raised bed guide · all topic guides →