Fertilizer NPK Numbers Table
| Grade (N-P-K) | N % | P₂O₅ % | K₂O % | Best for |
|---|---|---|---|---|
| 10-10-10 | 10 | 10 | 10 | All-purpose garden beds |
| 26-5-10 | 26 | 5 | 10 | Spring lawn feed |
| 5-10-5 | 5 | 10 | 5 | Flower beds and bulbs |
| 15-30-15 | 15 | 30 | 15 | Transplants and starters |
| 0-10-10 | 0 | 10 | 10 | Fall feed, no nitrogen |
| 6-12-12 | 6 | 12 | 12 | Root crops, low-N fall |
| 30-0-4 | 30 | 0 | 4 | Summer lawn with potash |
| 46-0-0 | 46 | 0 | 0 | Urea - pure nitrogen boost |
| 18-46-0 | 18 | 46 | 0 | DAP - phosphorus kick |
| 4-3-3 | 4 | 3 | 3 | Organic blend baseline |
The three numbers on every fertilizer bag are the percentages by weight of three nutrients - nitrogen (N), phosphate (P2O5) and potash (K2O) - and reading them is pure arithmetic: a 50-pound bag of 26-5-10 contains 13 pounds of actual nitrogen, 2.5 pounds of phosphate and 5 pounds of potash, with the remaining 29.5 pounds being filler that spreads the nutrients evenly. That is the whole secret the bag never states out loud, and it is why a 46-0-0 urea bag is nearly half pure nitrogen while a 4-3-3 organic blend is mostly carrier.
The grades are recipes, not ingredients: 10-10-10 is the all-purpose shorthand people reach for, 26-5-10 is a spring lawn feed front-loading growth, 5-10-5 tips the balance toward blooms and roots for flower beds, and 0-10-10 is the fall formula that skips nitrogen entirely so the lawn hardens off instead of pushing tender growth into frost. Matching the recipe to the plant's season - not doubling the dose - is what separates feeding from burning.
How to use
- Read the grade as N-P2O5-K2O by weight, always in that order: nitrogen first, phosphate second, potash third. A 10-10-10 is balanced; any number that leads (26-5-10) means growth-first; a fat middle number (15-30-15) is for roots and transplanting; a fat last number feeds fruiting and hardiness.
- Convert the numbers to pounds before buying: multiply the bag weight by each percentage. A 20-pound bag of 10-10-10 holds 2 pounds of each nutrient; the rest is granule carrier. Comparing price per pound of nitrogen (bag price divided by weight times N%) beats comparing bag prices.
- Match the grade to the calendar, not just the crop: nitrogen-heavy grades go on spring growth, balanced grades maintain mid-season, and fall feeding drops nitrogen (0-10-10 or 6-12-12) so perennials and lawns store energy instead of sprouting frost-tender shoots. One grade all year is the most common over-feeding mistake.
Frequently asked questions
What do the three numbers on fertilizer mean?
They are the weight percentages of nitrogen, phosphate (P2O5) and potash (K2O) - always in that order, and always the oxide forms for phosphorus and potassium rather than the bare elements, which is why the middle and last numbers look bigger once converted to elemental P and K. On a 50-pound bag of 26-5-10 you are buying 13 pounds N, 2.5 pounds P2O5 and 5 pounds K2O; the filler carries them and makes spreading even.
Is 10-10-10 good for everything?
It is the safe default for mixed beds because nothing dominates, but it is rarely optimal: lawns in spring want nitrogen-led 26-5-10, tomatoes and bulbs want the phosphorus-forward 5-10-5 or 15-30-15 class, and fall feeding wants little or no nitrogen. Using 10-10-10 everywhere is like seasoning every dish with the same mixed spice - edible, but half the plants are over-paying for nutrients they cannot use and the excess runs off.
How much 26-5-10 do I need per 1,000 sq ft?
The turfgrass rule is one pound of actual nitrogen per 1,000 square feet per application. At 26 percent nitrogen that takes about 3.8 pounds of product - so a 50-pound bag covers roughly 13,000 sq ft of lawn. Working backwards from a target nutrient, not forwards from bag size, is the only way the numbers on this chart become a real application rate.
What is 46-0-0 urea used for?
Pure nitrogen: 46 percent of the bag is urea nitrogen, the cheapest per pound there is. It powers leafy growth - lawns in peak season, corn, anything you are growing for leaves - but zero phosphate and potash means it feeds foliage without supporting roots, blooms or hardiness. It also volatilizes if left on dry soil, so it needs watering in, and it is the grade most often over-applied because the bag looks cheap until you do the per-nutrient math.
Why is phosphate written P2O5 and potash K2O?
Historical assay convention: fertilizers were analyzed by burning samples and weighing the oxides, so the labels stuck with the oxide even though the actual nutrients are elemental P and K. Converting: pure P is only 43.6 percent of P2O5, and pure K is 83 percent of K2O, which is why a soil test that says 'apply 1 pound of P' needs about 2.3 pounds of P2O5 from the bag. The chart above keeps the label convention so the numbers match what is printed.
Can I mix grades or switch mid-season?
Yes, and it is the intended pattern: start the season nitrogen-forward for growth, shift toward balanced as fruiting begins, and end with low-nitrogen fall grades. What you should not do is stack full doses - two spring feedings of 26-5-10 back to back put down twice the target nitrogen and burn. Calculate each application by its own nutrient target, and the grades become interchangeable tools rather than brands to be loyal to.