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The Dirt on Math: Calculators and Conversions for Gardeners

By Tamara Galbraith (TexasTamOctober 29, 2010

Let me start by saying that I was a journalism major in college. In other words, math has definitely never been my strong suit. So in the past, when it came to trying to figure out how many cubic yards I would need to cover 1500 square feet of garden bed with three inches of mulch, I feared my brain would explode. For those like me, fear no more, and rejoice in yet another reason why the Internet is so fabulous: online calculators.

Gardening picture

Measurement Converters

Before you schedule that delivery of a dump truck full of compost, figure out just what a "cubic yard" really is, because that's what most material companies use in measuring dry materials.

Volume Conversion: Online calculator

Cubic Feet and Yards:

27 Cubic feet = 1 Cubic yard = 1 Ton Avg. Dry Weight

Sq. ft. x deep divided by 324 = Cubic yards.


100 x 2" divided by 324 = .62 Cubic yards

400 x 3" divided by 324 = 3.70 Cubic yards


Even though the bottle gives the recipe for it, do you really need to mix up a gallon of Bt spray? Probably not. When diluting fertilizers and pesticides from concentrate, it's very important to measure accurately. When in doubt, use less than what is recommended by the manufacturer...never more.

One gallon = 4 Quarts/8 pints One cup = 1/2 pint/8 ounces/16 tablespoons

One gallon = 16 cups/128 ounces 1/2 Cup = 4 ounces/8 tablespoons/24 teaspoons

One gallon = 256 tablespoons/768 teaspoons 1/4 Cup = 2 ounces/4 tablespoons/12 teaspoons

One quart = 2 pints/4 cups/32 ounces/64 Tbls. 1 Tablespoon = 1/2 ounce/3 teaspoons

One pint = 2 cups/16 ounces/32 tablespoons

Area Conversion: Online calculator

Length/Distance: Online calculator

Weight and Mass: Online calculator


ImageOnline Calculators for Dry Materials

Fabulous calculators that take the guesswork out of some larger garden projects.

Mulch: How much mulch do you need for a certain-sized garden bed? Choose thickness and garden square footage.

Limestone: How much limestone do you need for a certain-sized garden bed? Requires that you know your soil's pH. Enter the pH, soil type and garden size. Limestone adds alkalinity to acidic soil, thus raising the pH.

Sulfur: How much sulfur do you need for a certain-sized garden bed? This calculator requires that you know your soil's pH. Enter the pH, soil type and garden size. Sulfur adds acidity to alkaline soil, thus lowering the pH.

Fertilizer: How much fertilizer should I spread on my lawn? Choose from several different types of fertilizers (blood meal, cow manure, 9-3-6, etc.) and grasses (Bermuda, bluegrass, fescue, etc.)

Calibrating your Fertilizer Spreader: Not an online calculator, but some good tips for figuring out the distribution rate of your rotary or drop spreader.

Actual Nitrogen in a bag of fertilizer. Choose the percentage of nitrogen shown on the bag and the weight of the bag.

Stone/Rock calculators (also gravel and Dry Quikrete Mix)

Bricks and Pavers


Online Calculators for Plants, Grass, Seed

Grass Seed

Plants (including perennials, annuals and groundcover), Grass Plugs, Shrubs and Trees: Very general - take with a grain of salt.

Sod Calculator: Calculates rectangular, circular and triangular areas.

Tree Height Calculator: How high is that tree?


Online Calculators for Water Features/Irrigation

Pond calculators based on pond shape (only works with Internet Explorer browsers): Calculates gallons of water, recommended filter, pump and liner sizes

Landscape Irrigation formulas, conversions and calculators: Includes calculators for area and distance, water pressure, flow and water volume, pump efficiency and more.


ImageMiscellaneous Online Calculators

Compost Mix Calculator: Helps design a compost recipe for many common household organic wastes. It will determine the Total C:N Ratio for a mix of materials.

Wind Chill

Illuminance (light): Especially handy for orchid growers, who often need to provide the correct "foot candle" measure of luminance.

How Many Lights Should I Put on My Christmas Tree?

Garden Math Sample Problems to make your brain explode


Smart Phone Apps - Converters, etc.


            Converter (Unit Converter): $0.99


            BlueSlate Unit Converter (Standard): Free


            ConvertPad: Free

All links will open in a new browser window. Links and link information were verified as accurate as of the date of article publication. All photos verified as public domain and obtained via Wikipedia.

  About Tamara Galbraith  
Tamara GalbraithI am an avid organic gardener and former Master Gardener for Collin County, Texas. I enjoy growing nearly everything, from vegetables to herbs to tropicals. Lately I have been converting the flower beds in my Zone 8 home to all Texas natives. In my non-gardening spare time, I enjoy cooking, reading, birdwatching or hugging on either my sweet English hubby or our Golden Retriever, Monty.

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