Gardening Calculators
Companion Planting Calculator
Look up whether two garden crops are a documented good, bad, or neutral companion-planting pairing, with the traditional reasoning behind each rating.
Compost Calculator
Turn a garden bed's area and target compost depth into cubic feet and cubic yards needed, with guidance on topdressing versus new-bed preparation depths.
Garden Fertilizer Calculator
Convert a target nitrogen application rate and a fertilizer's N-P-K percentage into the exact pounds of product needed for your garden bed or lawn area.
Garden Soil Calculator
Calculate the cubic feet and cubic yards of soil needed to fill a garden bed from its length, width, and depth, plus an estimated bag count for bagged soil.
Garden Watering Schedule Calculator
Convert the standard 1-inch-per-week watering guideline into exact gallons for your garden area, split across however many times a week you water.
Mulch Depth Calculator
Calculate the mulch volume needed for a garden area at a given depth, with guidance on the 2-4 inch range that avoids weed breakthrough or stem rot.
Plant Spacing Calculator
Calculate exactly how many plants fit a garden bed from its length, width, and spacing, with a grid layout and common crop spacing reference table.
Raised Bed Soil Calculator
Calculate total soil volume across multiple identical raised beds at once from bed dimensions, fill depth, and bed count, in cubic feet and cubic yards.
Seed Starting Date Calculator
Calculate the exact calendar date to start seeds indoors by counting back the recommended number of weeks from your area's average last frost date.
Tree Age Calculator
Estimate a standing tree's age from a trunk circumference or diameter measurement using published forestry growth factors for over 20 common species.
Planning a Garden Before the First Seed Goes In
Good gardens are planned with numbers as much as instinct — how much soil a raised bed actually needs, how far apart plants should sit to avoid competing for light and nutrients, and when to start seeds indoors relative to the local last frost date. Ten calculators here cover soil, spacing, and timing for a season of planning.
Popular Gardening Calculators
Ten tools span soil, spacing, and timing:
- Raised Bed Soil Calculator — converts bed dimensions into cubic feet or yards of soil mix needed to fill it.
- Plant Spacing Calculator — finds how many plants fit a given area at their recommended spacing.
- Seed Starting Date Calculator — works backward from the local last frost date to find when to start seeds indoors.
- Compost Calculator — balances carbon-rich and nitrogen-rich materials for an effective compost ratio.
- Companion Planting Calculator — suggests beneficial plant pairings based on established companion planting relationships.
Why Seed Starting Dates Work Backward From Frost
Seed packets list a recommended number of weeks to start seeds "before last frost," which means the actual calendar date depends entirely on a garden's local frost date — the same tomato variety might be started in early February in a warm climate and not until April further north. This is why seed starting calculators ask for a location or frost date rather than giving a single national date, and why using a generic calendar date instead of a frost-based calculation is one of the most common reasons transplants go out either too early (risking frost damage) or too late (shortening the growing season).
Frequently Asked Questions
Does compost really need a specific carbon-to-nitrogen ratio?
Yes — a ratio too high in nitrogen (too many "greens") produces a smelly, slow pile, while too much carbon (too many "browns") breaks down very slowly, so the roughly 25-30:1 carbon-to-nitrogen target actually affects how fast and how well a pile composts.
Why does plant spacing matter beyond just fitting more in?
Overcrowded plants compete for light, water, and nutrients, and reduced airflow between them raises the risk of fungal disease, so recommended spacing is about plant health as much as fitting a garden bed.
Explore More
Managing a larger agricultural plot? See the Agriculture Calculators, or plan outdoor hardscaping with the Landscaping Calculators.