Frost & Furrow

Garden math, done right — and sourced.

Free calculators for vegetable gardeners: when to start seeds, how much soil and mulch to buy, how to balance compost and fertilizer, and how much to water. Every formula is shown and every number is cited to university extension services.

No sign-upWorks on your phoneFormulas shownExtension sources

Plan my seed starting →

All tools

Timing

Seed starting calculatorIndoor sowing, transplant and direct-sow dates for 33 crops from your last frost date.Fall planting calculatorThe latest date to sow a fall crop, using the extension "Fall Factor" method.

Soil & beds

Raised bed soil calculatorCubic feet, yards, liters and bags for any number of rectangular or round beds.Square foot garden plannerPlants per square (1/4/9/16), squares needed and a quick visual layout.Plant spacing calculatorHow many plants fit at a given spacing — square grid vs. staggered rows.Mulch calculatorCubic yards and bags of mulch for any bed and depth.

Feeding & compost

Compost C:N ratio calculatorCarbon-to-nitrogen ratio and moisture of your mix, with a fix to reach 30:1.Garden fertilizer calculatorPounds, ounces and cups of any N-P-K product for your area.

Water

Garden watering calculatorGallons per week from the 1-inch rule, minus rain, plus hose run time.Rain barrel calculatorGallons collected from your roof per rain and how many barrels it fills.

How these tools are built

Each calculator starts from a published method — mostly U.S. land-grant university extension services such as University of New Hampshire, Virginia Tech, Iowa State, Cornell, University of Minnesota and University of Nebraska–Lincoln. The formula is printed under every calculator with a worked example from the source, and automated tests check the math against those examples.

The tools run entirely in your browser. Nothing you type is sent anywhere.