University of Missouri Extension

WQ551, New November 1994

Calibrating Home Garden Equipment

Dennis S. Schrock
Department of Horticulture

Quick facts

Proper use of fertilizers and pesticides, whether of synthetic or natural origin, contributes to healthy plant growth. Applying too much may cause foliar burns or other toxic reactions in the plant. Using too little may result in damaged plants from inadequate pest control or nutrient deficiencies.

The only way to know just how much fertilizer or pesticide is being applied to the plants in your yard is to calibrate the application equipment. Calibrating an applicator is relatively simple.

This guide outlines the steps for calibrating sprayers used for liquid applications (Figure 1) and lawn spreaders used for dry products (Figure 2). Always read and follow the product label.

Canister and hose-end sprayers Figure 1
Either canister sprayers, left, or hose-end sprayers, right, may be used for liquid applications of fertilizers and pesticides.

Rotary and a drop spreader Figure 2
Granular fertilizers, pesticides or combination products are applied with either a rotary spreader, left, or a drop spreader, right.

Steps in calibrating a sprayer

If you sprayed a band 16 feet wide by 50 feet long, you covered 800 square feet: 16 feet x 50 feet = 800 square feet. You may want to repeat steps two through five a few times until you get consistent readings.

Canister sprayer example
One quart of spray covered 800 square feet. That means 4 quarts (1 gallon) of spray will cover 3,200 square feet.

Hose-end sprayer example
One-half cup of water in the concentrate container covered 1,200 square feet when diluted. 1/2 cup = 24 teaspoons, so each teaspoon covered 50 square feet (1,200/24).

Table 1
Useful measurements and conversions


Liquid measure

Quick conversions

Liquid calibration tips

Steps in calibrating a drop spreader

If no settings are provided on the product bag or in the owner's manual, try adjusting the opening of the spreader to where it is slightly larger than the product particles.

If it is more convenient to apply fertilizer by volume measure than to weigh it, the conversion factors shown in Table 2, may be helpful.

Sweep up and reuse the material regardless of method used.

Swept up 5 quarts (= 10 pints) of 10-10-10 fertilizer from 1,000 square feet. That equals 10 pounds of product per 1,000 square feet. If the area used for calibration was 500 square feet, double the answer to get the rate per 1,000 square feet.

We want to apply one pound of actual nitrogen per 1,000 square feet. A 10-10-10 fertilizer supplies 10 percent nitrogen (the first number). Therefore, 10 pounds of the fertilizer provides 1 pound of nitrogen, which is what we want. No adjustments are necessary.

Table 2
Weight per volume relationship of fertilizer and lime

Material Pounds Pints1
Mixed fertilizers such as 10-6-4, 10-10-10
Ammonium sulfate (21-0-0)
Muriate of potash (6-0-60)
Superphosphates (0-20-0; 0-46-0)
1 1 20-10-10, etc.
Processed manure
Ureaformaldehyde (38-0-0)
Urea (0-45-0)
Ammonium nitrate (33-0-0)
1 1-1/3
Potassium sulfate,
1 3/4
1For smaller quantities, remember 1 pint equals 2 cups or 32 level tablespoons.

Steps in calibrating a rotary spreader

Twenty-four-can soda boxes are about the right size to use. Space the boxes uniformly across an area slightly wider than the spreader throws the product. Measure the distance between boxes, and make a note of it.

In most cases, the containers in the middle will be fuller than those on the edges. Remember to sweep up and reuse the material not caught in the boxes.

Granular calibration tips

Partial funding for this publication provided by U.S. EPA, Region VII.
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