Fertilizer NPK Calculator
Turn a soil test into pounds of nutrients per bed.
Use ToolFree calculator
Fertilizer Blend Solver
Mix bagged fertilizers into a blend that hits your exact N-P-K target: enter the pounds of nitrogen, phosphate and potash you want, pick two or three products, and the solver finds the closest match and its cost.
Fertilizer Blend Solver
Chlorova · updated for 2026
Fertilizer Blend Solver
Choose two or three products and hit “Solve blend” to fit your N-P-K target.
The solver balances nutrient percentages against your entered target; it does not judge whether that target is agronomically correct for your crop or soil, and it assumes each product's labeled guaranteed analysis is accurate and fully plant-available. Prices are typical bag rates for comparing blends, not live quotes, and nutrient availability, soil pH and application timing are outside its scope. Confirm your actual rates with a soil test and local extension guidance, and never exceed recommended nitrogen in a single application to avoid burning the crop or leaching nitrate.
Mixing your own fertilizer from bagged products is cheaper and more flexible than buying a pre-blended grade, but hitting an exact N-P-K target with a few ingredients is fiddler math most gardeners would rather skip. This solver does that optimization in your browser: type the nitrogen, phosphorus and potassium you want per thousand square feet, choose two or three products from a common list, and it grid-searches the amounts that land closest to your target. It reports how many pounds of each to use, the nutrients actually delivered against what you asked for, and the blend cost.
Getting a Usable Blend in a Few Clicks
- Enter the nitrogen, phosphate and potash you want per thousand square feet.
- Set your bed or lawn area in square feet.
- Choose product A from the drop-down list of common fertilizers.
- Add product B, and optionally product C, to widen the nutrients you can reach.
- Tick prefer-cheapest if cost matters more than a razor-close nutrient match.
- Press Solve blend to search the amounts that fit your target.
- Read the pounds of each product and the nutrients actually delivered.
- Adjust the product choices if the fit looks loose and solve again.
How the Solver Matches Your N-P-K Target
Fertilizer labels quote three percentages: nitrogen as N, phosphorus as phosphate P2O5, and potassium as potash K2O. The solver turns your target into product weight with one identity, pounds of nutrient equals pounds of product multiplied by the nutrient percentage divided by one hundred. A pound of 46-percent urea thus carries roughly 0.46 pound of nitrogen, so a two-pound nitrogen target needs somewhere near four and a half pounds of it.
Because a blend must balance three nutrients at once with only two or three ingredients, there is no single dividing step that gives the answer, so the tool sweeps a grid of plausible amounts for each product, scores every combination by how far its nitrogen, phosphate and potash fall from your targets, and keeps the closest. Oversupply is penalized like undersupply, so it will not dump extra salt to chase one number. Enable the cheapest option and, among equally close blends, it keeps the lowest-cost one instead.
Worked Example: Hitting a 2-1-2 Target on a Thousand Square Feet
- Set target nitrogen to 2, phosphate to 1 and potash to 2 pounds.
- Leave the area at 1,000 square feet so the targets apply directly.
- Choose product A as MAP 11-52-0 to carry the phosphorus.
- Set product B to sulfate of potash 0-0-50 for the potassium.
- Set product C to urea 46-0-0 to finish the nitrogen.
- Press Solve blend to search the closest matching amounts.
- About 1.9 pounds of MAP supplies the pound of phosphate.
- That same MAP adds a little nitrogen, so urea covers the rest.
- Roughly 4 pounds of potash meets the 2-pound potash target.
- The readout shows delivered versus target nutrients and the total cost.
Common Products and What They Supply
The fertilizer products the solver can mix, with the guaranteed analysis and the nutrient each is really chosen for.
| Product | Analysis | Main nutrient it adds |
|---|---|---|
| Urea | 46-0-0 | Nitrogen |
| Ammonium sulfate | 21-0-0 | Nitrogen, sulfur |
| DAP | 18-46-0 | Phosphate, some nitrogen |
| Muriate of potash | 0-0-60 | Potash |
| Sulfate of potash | 0-0-50 | Potash |
| Blood meal | 12-0-0 | Organic nitrogen |
| Bone meal | 1-11-0 | Phosphate |
| Composted chicken manure | 6-3-3 | Balanced organic |
| Garden compost | 1-1-1 | Fertility, low numbers |
Key Terms
- Guaranteed analysis
- The three legally required nutrient percentages printed on every fertilizer bag.
- N-P-K
- The label ratio of nitrogen, phosphate and potash in that order.
- Phosphate (P2O5)
- The middle number, the standard way fertilizer phosphorus is reported.
- Potash (K2O)
- The last number, the standard way fertilizer potassium is reported.
- Blend search
- Testing many amount combinations to find the closest fit to your target.
- Elemental
- The pure nutrient amount, not the carrier it happens to be mixed into.
Blending Habits That Save Money and Salt
- Start from a soil test, not a guess, because a blend tuned to a target you do not actually need just wastes money and can burn the crop.
- Organic products carry low, variable numbers, so matching a synthetic target with them means far more pounds and a looser fit the solver will flag.
- Two well-chosen products usually reach a target better than three haphazard ones, since each extra ingredient gives the search another lever and another cost.
- Phosphate and potash rarely move far in soil, so band them at planting, while nitrogen is the number to re-check and split across the season.
- If the fit stays loose, you are missing a nutrient source entirely; swap in a potash or phosphate product rather than piling on more urea.
Common Mistakes and Fixes
- Chasing a decimal-point-perfect nutrient match when a close, far cheaper blend would do the job.
- Loading up nitrogen because it is cheap, then over-salting the bed and still under-feeding phosphate.
- Forgetting the area scaling and applying a per-thousand-square-foot rate to a whole acre plot.
- Assuming the organic label means the numbers match the synthetic grades they are meant to replace.
- Mixing products that tie up a nutrient, then wondering why the plants never take it up.
- Ignoring the loose-fit warning and spreading the blend anyway at the wrong final rate.
When to Use This and When Not To
Use this solver when a soil test or a planting plan has handed you specific nitrogen, phosphate and potash goals and you want to meet them from bagged products you can actually buy. It is a matching tool, not an agronomic prescription, so it will not tell you whether 2 pounds of nitrogen is the right number; get that from the fertilizer and soil-test calculators. Skip it if you only need one product, where the simple NPK calculator is a quicker answer.
Fertilizer Blend Solver: Frequently Asked Questions
Why can't the blend hit my target exactly?
Because three nutrients must balance from only two or three ingredients, the amounts rarely solve perfectly, so the tool returns the closest fit and shows the delivered versus target numbers. Choosing products that together cover all three figures tightens that match considerably.
Is a cheaper blend always the better choice?
Not if it misses the nutrient you actually needed. The cheapest toggle only picks the lowest-cost blend among options that fit your target about equally well, so it saves money without quietly underfeeding a number you set on purpose.
Do organic fertilizers work in this solver?
Yes, the product list includes blood meal, bone meal, composted manure and compost, but their low percentages mean you apply far more pounds for the same nutrient. The blend still fits, just with bigger volumes and a looser match than a concentrate.
How accurate are the prices it uses?
The per-pound costs are typical bag prices, not live quotes, so treat the blend cost as a comparison between options rather than a receipt. Actual prices swing by brand, region and bag size, though the cheapest-versus-closest ranking usually still holds. Judge a blend on cost per nutrient delivered, not on the sticker price of one bag.
What if there is no good blend at all?
Then your chosen products cannot supply the nutrients you want, and the tool flags a loose fit. Add a product that carries the missing element, or relax an unrealistic target, and re-solve rather than spreading a blend that never matched what your plants need.
Sources & Further Reading
- Fertilizer Selection and Nutrient Recommendations — Iowa State University Extension and Outreach. Guaranteed-analysis percentages and the per-area nutrient-rate method the solver mirrors.
- Soil Testing and Fertilizer Use for Home Lawns and Gardens — Penn State Extension. Basis for targeting N-P-K from a soil test rather than guessing at rates.
- Organic and Specialty Fertilizer Materials — University of Florida IFAS Extension. Analysis ranges for the manure meals, potashes and composts in the product set.
Chlorova Gardening Team
Builds, checks and documents every tool we publish
Chlorova editorial review
Checked against extension-service publications
Formula verified against published references · Updated
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