Free Garden Calculators
Stop guessing. Balance your compost pile, fill your raised beds, spread the right amount of mulch and fertilizer โ with fast, free garden calculators built on standard horticultural math.
Compost C:N Ratio Calculator
Mix browns and greens by weight to hit the ideal 25โ30:1 carbon-to-nitrogen ratio for fast, hot composting.
Raised Bed Soil Calculator
How much soil do you need? Enter bed dimensions to get cubic feet, cubic yards, bag counts and a Mel's Mix recipe.
Mulch Calculator
Find how many cubic yards and bags of mulch you need from your bed dimensions and target depth.
Seed Spacing Calculator
Enter bed size and plant spacing to see exactly how many plants fit โ no overcrowding, no wasted space.
Lawn Fertilizer Calculator
How much fertilizer per 1000 sq ft? Enter your lawn area and N-P-K to get the exact pounds to spread.
Compost Needed Calculator
How much compost do you need for top-dressing? Get cubic yards, cubic feet and bag counts from bed size.
Rainwater Harvesting Calculator
How much rain can your roof collect? Enter roof area and rainfall to get gallons and liters of harvestable water.
Pond Calculator
Planning a garden pond? Get water volume in gallons and the exact liner size to buy from length, width and depth.
Drip Irrigation Calculator
How much water does each watering use? Enter emitter count, flow rate and run time to get gallons per watering.
Potting Mix Calculator
How much potting soil do your containers need? Enter pot diameter and height to get liters, cubic feet and dry quarts.
Liquid Fertilizer Calculator
Mix liquid feed by ppm, not spoonfuls. Enter target nitrogen, fertilizer N% and water volume for exact grams to add.
Planting Calendar Calculator
Pick your USDA zone or enter your last frost date to get indoor seed-starting and outdoor planting dates for 10 common vegetables.
Soil pH Calculator
How much lime or sulfur? Enter bed area, current and target pH, and soil type for exact amendment rates.
Growing Guides
Step-by-step guides that go deeper than the calculators โ the why behind the numbers.
Compost C:N Ratio Explained
Why 25โ30:1 works, a C:N table for 12 materials, a worked mixing example, and troubleshooting for smelly or stalled piles.
Vegetable Planting Calendar Guide
What frost dates mean, how to find yours, succession planting, and fall garden planning โ with worked zone examples.
Why use garden calculators?
Most garden frustrations โ a compost pile that never heats up, a raised bed that costs a fortune to fill, a lawn burned by too much fertilizer โ come from the same root cause: guessing instead of calculating. Each of our calculators replaces a guess with simple math backed by widely accepted horticultural guidelines, from the 25โ30:1 compost C:N ratio to the standard 1 lb of nitrogen per 1000 sq ft for lawns.
Whether you're building your first raised bed, starting a backyard compost bin, or fine-tuning an established vegetable garden, running the numbers first saves you money, materials and growing seasons.
Start composting in 5 steps
- Pick a spot with good drainage and partial shade, at least a few feet from fences or structures.
- Gather greens and browns โ kitchen scraps and grass clippings for nitrogen, dry leaves and cardboard for carbon.
- Balance the pile with the compost C:N ratio calculator โ aim for 25โ30:1.
- Keep it moist like a wrung-out sponge and turn it every 1โ2 weeks to add oxygen.
- Harvest and spread finished compost on your beds โ the compost needed calculator tells you how much.