Spray Mix Calculators Liquid Fertilizer Rate Calculator

Liquid Fertilizer Rate Calculator

Calculate the exact liquid fertilizer application rate needed to deliver a target amount of nitrogen, phosphorus, or potassium. Enter the NPK analysis and fertilizer density from your label — get gallons per acre, oz per 1,000 sq ft, and lbs of each nutrient delivered. Works for broadcast, foliar, fertigation, and small-container garden applications.

⚠️ Base rates on a current soil test.

This calculator computes how much fertilizer delivers a target nutrient rate. It does not prescribe what rate to apply. Always use a soil test recommendation and follow the product label's minimum and maximum rates.

On this page: Calculator · Reading NPK labels · Common liquid fertilizer reference · Application rate guide · Related tools · FAQ

Applying fertilizer with a sprayer? Sprayer Calibration Calculator · Adding fertilizer to a tank mix? Tank Mix Calculator.

Calculator

Liquid Fertilizer Application Rate Calculator

Choose a mode: Rate Finder to calculate gal/acre from a target nutrient rate · Nutrient Checker to see lbs of N-P-K delivered by a given application rate · Small-Scale Container for 5-gallon buckets, backpack sprayers, and garden use.

Enter your fertilizer analysis and target nutrient rate to find the required application rate in gallons per acre and oz per 1,000 sq ft.

Fertilizer Product

Target Nutrient Rate

Already know your application rate? Enter it here to see exactly how many lbs of N, P₂O₅, and K₂O you're delivering per acre or per 1,000 sq ft.

Application Rate Applied

For garden, lawn, or small-scale use. Enter your target area, fertilizer NPK, and container size to get oz or tablespoons per container — including 5-gallon bucket and backpack sprayer amounts.

Target & Container

Tip: For precise small-volume measuring, use a measuring syringe or graduated cylinder.

🌱 Applying liquid fertilizer with a sprayer?
Make sure your equipment is dialed in: Sprayer Calibration Calculator · Spray Tip Calculator · Nozzle Flow Rate Calculator.

How to read liquid fertilizer NPK labels

Every liquid fertilizer label includes a guaranteed analysis expressed as three numbers: N – P₂O₅ – K₂O. Understanding what these mean is essential to calculating the correct application rate.

Number Nutrient Form reported What it means
First (N) Nitrogen % elemental N by weight 28-0-0 contains 28 lbs of N per 100 lbs of product
Second (P) Phosphorus % as P₂O₅ by weight To convert to elemental P: multiply by 0.436
Third (K) Potassium % as K₂O by weight To convert to elemental K: multiply by 0.830

Why weight per gallon matters

Because liquid fertilizers are applied by volume (gallons per acre), you must know the weight per gallon (lbs/gal) to convert between volume and nutrient weight. This varies significantly by product: water weighs 8.34 lbs/gal, while 28-0-0 UAN weighs 10.86 lbs/gal and 10-34-0 APP weighs 11.65 lbs/gal. Always find this on the product label — using the wrong density leads to significant over- or under-application.

The core formula this calculator uses:

Gal/acre = Target lbs nutrient/acre ÷ (Nutrient% ÷ 100 × lbs/gal)

Example: to apply 100 lbs N/acre with 28-0-0 UAN at 10.86 lbs/gal:
100 ÷ (0.28 × 10.86) = 100 ÷ 3.04 = 32.9 gal/acre

Common liquid fertilizer reference chart

Reference values for widely used liquid fertilizers. Always verify NPK and density against your specific product label — formulations vary by manufacturer and region.

Product Analysis (N-P₂O₅-K₂O) Weight (lbs/gal) Lbs N per gal Common use
28-0-0 UAN 28-0-0 10.86 3.04 Sidedress N; pre-plant corn, wheat
32-0-0 UAN 32-0-0 11.06 3.54 Higher-N applications; lower volume per acre
30-0-0 UAN 30-0-0 10.96 3.29 Broadcast N; broadcast or injection
10-34-0 APP 10-34-0 11.65 1.17 Starter fertilizer; pop-up; in-furrow P
11-37-0 APP 11-37-0 11.63 1.28 Starter fertilizer; high-P starter
9-18-9 9-18-9 10.70 0.96 Complete starter; row-crop planting
0-0-60 KTS 0-0-60 11.11 0 Potassium thiosulfate; K + S source
20-10-10 20-10-10 10.80 2.16 Complete blend; turf, vegetables
4-3-6 organic 4-3-6 8.70 0.35 Organic-based; garden, ornamentals

⚠️ Reference only. Product density and analysis vary by manufacturer. Always use the values on your specific product label.

Liquid fertilizer application rate guide by crop and use

These are general nitrogen rate guidelines. Actual rates should be based on soil test results, yield goals, and local agronomic recommendations. Phosphorus and potassium rates follow similar principles but depend heavily on soil test levels.

Application Type Typical N Rate Notes
Corn — pre-plant / sidedress 100–200 lbs N/acre Split application recommended; sidedress at V4–V6
Winter wheat — topdress 60–120 lbs N/acre Apply at Feekes 4–6; UAN streamed preferred over broadcast
Soybeans — starter 20–40 lbs N/acre Low N rate; mainly for P and K starter in-furrow
Turf / lawn 0.5–1.0 lb N/1,000 sq ft Per application; 4–6 applications per season typical
Vegetables — broadcast 0.1–0.3 lb N/1,000 sq ft Per application; more frequent at lower rates preferred
Foliar — crop canopy 3–10 lbs N/acre per pass Low rate; used as supplement, not primary N source
Fertigation — drip Varies by crop + stage Weekly or daily injection; match to crop uptake curve
Starter — in-furrow (10-34-0) 2–5 gal/acre Rate-limited by salt index; check safe rate for crop

Foliar burn risk: Liquid fertilizers applied to foliage can cause burn, especially UAN above 2–3% solution or at temperatures above 85°F. Dilute to below 1% N solution for most foliar passes. The Small Container tab calculates the dilution ratio for any concentration target.

Frequently asked questions

How do you calculate liquid fertilizer application rate?

The formula is: Gal/acre = Target lbs nutrient/acre ÷ (Nutrient% ÷ 100 × lbs/gal). For 28-0-0 UAN (10.86 lbs/gal) to deliver 100 lbs N/acre: 100 ÷ (0.28 × 10.86) = 32.9 gal/acre. The Rate Finder tab does this automatically for any NPK analysis, density, and nutrient target.

How much liquid fertilizer do I add to a 5-gallon bucket?

It depends on your target nutrient rate and the area you're treating. Use the Small Container tab above: enter the fertilizer NPK, target N rate (e.g., 0.5 lbs N per 1,000 sq ft for lawns), and your area in square feet — the calculator shows exactly how many fl oz to add to a 5-gallon bucket. As a rough guide, a 20-10-10 fertilizer at a typical lawn rate requires about 4–8 fl oz per 5 gallons depending on the area covered.

How much liquid fertilizer should I give my plants?

Rates vary by plant type and growth stage. General guidelines: lawns receive 0.5–1.0 lb N per 1,000 sq ft per application; vegetable gardens receive 0.1–0.3 lb N per 1,000 sq ft; potted plants follow label directions (typically 1/4 to 1/2 strength of the label rate for regular applications). Start at the lower end and adjust based on plant response. Never exceed the label maximum rate in a single application — this risks fertilizer burn.

What does NPK mean on liquid fertilizer?

NPK stands for the three primary macronutrients: N (Nitrogen), P (Phosphorus, reported as P₂O₅), and K (Potassium, reported as K₂O). The guaranteed analysis numbers on the label are percentages by weight. A product labeled 28-0-0 contains 28% nitrogen by weight, no phosphorus, and no potassium.

Why does weight per gallon matter for liquid fertilizer calculations?

Liquid fertilizers are applied by volume (gallons), but nutrient content is expressed by weight (lbs). The weight per gallon connects the two. Using the wrong density value causes significant errors — for example, assuming water density (8.34 lbs/gal) for 28-0-0 (10.86 lbs/gal) would underestimate N delivery by 23%. Always find the exact weight per gallon on your product label.

Can I mix liquid fertilizer with herbicide or pesticide in the same tank?

Many liquid fertilizers are compatible with herbicides and pesticides, but not all combinations work. UAN (28-0-0 or 32-0-0) is commonly tank-mixed with glyphosate, but can antagonize some ALS-inhibitor herbicides. 10-34-0 can cause precipitation with certain calcium-containing products. Always do a jar test before filling a full tank. Use the Tank Mix Calculator to plan amounts, and the Mixing Order Guide for the correct addition sequence.

What is fertigation and how do I calculate the rate?

Fertigation is applying liquid fertilizer through an irrigation system — drip tape, microsprinklers, or center pivots. Rates are typically expressed as lbs nutrient per acre per injection event or per week. Use the Rate Finder tab to calculate how many gallons of fertilizer to inject per acre per event, then scale to your total irrigated area with the Acres mode. Injection rates must stay within the system's safe fertilizer concentration limits (typically <0.5% N by solution weight) to avoid equipment corrosion and emitter clogging.