🌱 Soil & Medium Volume Calculator
Calculate how much soil, coco coir, or perlite you need for any container size
Calculate Your Medium Volume
Inside diameter of the pot
Inside height of the pot
Standard fabric pot gallon sizes
Enter total volume per container in gallons
How many containers are you filling?
Your Soil Volume Results
Bags Needed:
Amendment Suggestions:
THE MORE YOU KNOW: Growing Media for Cannabis
Potting Soil
Pre-mixed potting soil is the easiest option for beginners. It contains organic matter, perlite for drainage, and often slow-release nutrients. Look for soils specifically formulated for cannabis or high-performance plants. Potting soil retains moisture well, which means less frequent watering but also a higher risk of overwatering.
Coco Coir
Coco coir is a renewable byproduct of coconut processing. It provides excellent aeration and drainage while retaining moisture well. Coco is pH neutral (5.5-6.5) and is considered an inert medium, meaning you have full control over nutrient delivery. It is popular among intermediate to advanced growers who prefer hydroponic-style feeding schedules.
Perlite
Perlite is a volcanic glass that is heated to create lightweight, porous white particles. It improves drainage and aeration when mixed with soil or coco coir. Pure perlite is rarely used alone for cannabis but is essential as an amendment. A 70/30 coco/perlite mix is one of the most popular growing media for cannabis.
Container Size and Plant Growth
Container size directly impacts plant size and yield. A general guideline for cannabis is 2 gallons of medium per foot of expected plant height. Seedlings start in small containers (solo cups or 1-gallon pots) and are transplanted up as they grow. Most indoor grows use 3 to 7 gallon containers, while outdoor plants may need 15 to 25 gallons or more for full-size plants.
Drainage and Aeration
Proper drainage is critical for healthy cannabis roots. Without adequate drainage, roots become waterlogged and susceptible to root rot. Fabric pots naturally provide excellent aeration through air pruning, where roots are exposed to air at the pot walls and naturally stop growing outward, encouraging a denser root ball instead of root-bound circling.
HOW TO USE THIS Calculator
- Select your container type (round pot, square pot, fabric pot, raised bed, or enter a custom volume)
- Enter the dimensions of your container or select a standard fabric pot size
- Enter the number of containers you plan to fill
- Select the growing medium you will be using
- Click "Calculate Volume" to see total volume, weight, and bag estimates
- Review the amendment suggestions for your chosen medium
- Use the cubic feet measurement when purchasing bagged soil at the store
CALC'S FAQ HOTLINE
How much soil do I need for a 5-gallon fabric pot?
A 5-gallon fabric pot requires approximately 5 gallons (about 0.67 cubic feet) of growing medium. Since fabric pots have flexible sides, you may want to add 10-15% extra to account for settling. One standard 1 cubic foot bag of soil will fill about one and a half 5-gallon pots.
What is the best growing medium for cannabis?
The best medium depends on your experience and growing style. Potting soil or super soil is great for beginners as it contains nutrients. Coco coir mixed with perlite (70/30) is popular for intermediate growers who want more control over feeding. Pure coco coir is preferred by advanced growers using hydroponic-style nutrient schedules.
Is this tool free to use?
Yes! This tool is completely free with no hidden costs, subscriptions, or limitations. Use it as often as you need.
Do I need to create an account?
No account needed. The tool works entirely in your browser without requiring signup or personal information.
Is my data private?
Absolutely. All processing happens locally in your browser. Your data never leaves your device and is not stored on any server.
How much does wet soil weigh compared to dry soil?
Wet soil typically weighs about 1.5 times more than dry soil. For example, if your dry potting soil weighs 12 lbs per gallon, it will weigh approximately 18 lbs per gallon when fully saturated. This is important to consider for shelving, balconies, and structural support.