Calculate how much fertilizer you need, how much nutrient a product rate supplies, or which fertilizer is the better buy.
Enter target nutrient rate, fertilizer grade, area, and optional bag size to calculate product rate, total material, bag count, cost, and incidental N-P-K supplied.
Inputs & Parameters
Enter target nutrient rate, fertilizer grade, area, and optional bag size to calculate product rate and total material.
Bag and cost options
Use a soil test recommendation
Optional soil-test conversion appears here.
Products to compare
Area helper
Enter dimensions to convert area.
Results
Enter a fertilizer grade and target nutrient to calculate product, bags, cost, and incidental nutrients.
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Interpretation—
Product rate equals the nutrient target divided by the nutrient fraction in the fertilizer grade.
Incidental nutrients supplied
Nutrient
Per acre
Per 1,000 sq ft
Total
Calculate to see N, P2O5, and K2O supplied.
Comparison table
Product
Product rate
Total product
Bags
Total cost
Cost/lb target nutrient
Nutrients supplied
Use Compare fertilizers mode to compare up to three products.
How Fertilizer Application Rate Works
Fertilizer Application Rate Calculator converts a soil-test or label recommendation into the fertilizer product rate you actually spread. It also works in reverse: enter a product rate and fertilizer grade to see the N, P2O5, and K2O supplied.
The calculator supports farm rates, lawn rates, and metric small-area work: lb/acre, kg/ha, lb per 1,000 sq ft, oz per 1,000 sq ft, g per square meter, and kg per 100 square meters. Optional bag and price fields turn the agronomic rate into a purchase estimate with bags, leftover product, and cost per acre or per 1,000 sq ft.
All calculations run in your browser. Field size, bag price, and fertilizer choices are not uploaded.
Formulas
Nutrient fraction = label percentage ÷ 100. A 46-0-0 fertilizer contains 0.46 lb N per lb of product.
Total product = product rate per acre × acres treated.
Bags needed = total product ÷ bag weight. Round up when buying whole bags.
Estimated cost = bags to buy × price per bag. Cost per acre = total cost ÷ acres; cost per 1,000 sq ft = total cost ÷ treated thousand-square-foot units.
Small-area conversion = lb/acre ÷ 43.56 for lb per 1,000 sq ft. Multiply lb per 1,000 sq ft by 16 for oz per 1,000 sq ft.
Metric conversion = lb/acre × 1.12085 for kg/ha. One g/m2 equals 10 kg/ha, which equals 8.92179 lb/acre.
P2O5 and K2O note: fertilizer labels usually report phosphorus as available phosphate (P2O5) and potassium as soluble potash (K2O). Do not treat those values as elemental P or K unless your recommendation explicitly asks for elemental units.
Worked Examples
120 lb N/acre with 46-0-0 urea
120 ÷ 0.46 = 260.9 lb product per acre. On 40 acres, that is 10,435 lb total, or about 209 bags at 50 lb each.
1 lb N/1,000 sq ft with 25-5-10
1 ÷ 0.25 = 4 lb product per 1,000 sq ft. The same rate also supplies 0.2 lb P2O5 and 0.4 lb K2O per 1,000 sq ft.
Convert 10-10-10 recommendation to 20-0-0
If a soil test says 500 lb/acre of 10-10-10, the N supplied is 50 lb/acre. A 20-0-0 product needs 50 ÷ 0.20 = 250 lb/acre to match the nitrogen, but it will not supply the P2O5 or K2O from the original recommendation.
Bags for a 5,000 sq ft lawn
At 1 lb N/1,000 sq ft with 25-5-10, use 4 lb product per 1,000 sq ft. For 5,000 sq ft, total product is 20 lb, so one 40 or 50 lb bag is enough with leftover material.
FAQs
How much 46-0-0 per acre for 120 lb N?
Use 120 ÷ 0.46 = 260.9 lb of 46-0-0 product per acre.
How much fertilizer for 1 acre?
Divide the target nutrient rate per acre by the nutrient fraction in the fertilizer grade. For example, 60 lb N/acre with a 30% N product needs 200 lb product per acre.
How do I convert lb per acre to lb per 1,000 sq ft?
Divide by 43.56. A 174.2 lb/acre product rate equals 4.0 lb per 1,000 sq ft.
What does 10-10-10 mean?
It means 10% nitrogen, 10% available phosphate as P2O5, and 10% soluble potash as K2O by product weight.
Can I use this for lawns?
Yes. Select lb per 1,000 sq ft or oz per 1,000 sq ft, enter lawn area, and add bag weight to estimate how many bags to buy.
Why are phosphorus and potassium shown as P2O5 and K2O?
Those are standard fertilizer-label conventions. Soil tests and labels often use P2O5 and K2O instead of elemental P and K.
How many bags do I need?
Total product divided by bag weight gives exact bags. For shopping, choose round up to whole bags so the estimate includes enough material for the treated area.
Should I fertilize without a soil test?
A soil test is the best starting point, especially for phosphorus, potassium, lime, and pH decisions. Without a test, avoid high rates and follow local extension and label guidance.
Practical Fertilizer Guidance
1
Do not apply at the wrong time
Avoid application before heavy rain, on frozen or saturated soil, during drought stress, or where label restrictions and local nutrient rules say not to apply.
Timing
2
Start with soil testing
Soil tests reduce guesswork and are especially important for phosphorus, potassium, pH, lime, and fields or lawns with a history of overapplication.
Soil test
3
Read the fertilizer label
The N-P-K grade is a percentage by weight. A 50 lb bag of 10-10-10 contains 5 lb N, 5 lb P2O5, and 5 lb K2O.
Label
4
Calibrate the spreader
Calculator output is only the target. Check the spreader pattern, swath width, ground speed, and actual material used on a known area.
Calibration
5
Protect water quality
Keep fertilizer off pavement, maintain buffers near water, sweep granules back onto turf or soil, and avoid applying where runoff is likely.
Runoff
Calculation Basis
Reviewed guidance: This calculator follows common extension-style fertilizer conventions: N-P-K labels are weight percentages, phosphate and potash are reported as P2O5 and K2O, product rate equals nutrient target divided by nutrient fraction, and application planning should be checked against soil-test recommendations, product labels, and calibrated equipment.
Last updated: June 23, 2026. Editor: Starlight Tools editorial team.
