Pot Volume Calculator: Gallons, Litres, Cubic Feet — Instant Results for Any Container
What this page answers: How to calculate the volume of any plant pot in gallons, litres, quarts, and cubic feet. Includes a full pot size chart by diameter, unit-conversion tables, soil fill amounts, grow bag sizes, metric nursery pot volumes, and 30+ gardener FAQs.
You are standing at the garden centre with a bag of potting mix in one hand and a new container in the other. You have no idea whether one bag is enough. Sound familiar?
Or maybe you are ordering grow bags online and need to know exactly how many gallons a 16 inch pot holds before you add it to your cart.
Either way, our pot volume calculator gives you the answer in seconds — in gallons, litres, quarts, or cubic feet. This guide explains the formula, provides a full pot size reference chart, covers every common unit conversion, and answers more than thirty questions that gardeners search for every single day.
Once you know your pot’s volume, jump straight to our soil calculator for pots to turn that number into a precise shopping list.
What Is a Pot Volume Calculator and Why Do You Need One?
A pot volume calculator is a tool that computes the internal capacity of a plant container using its diameter and depth. It converts the result into the units you need — US gallons, litres, quarts, or cubic feet — so you can buy exactly the right amount of potting mix and choose the right size container for any plant.
Without it, you are guessing. Guessing costs you money on wasted soil, time on return trips to the garden centre, and — most importantly — plant health when the wrong pot volume causes waterlogging or root cramping.
Here is what pot volume controls directly:
- Root development. Roots need proportionate space. Too little space = root-bound stress. Too much space = oversaturated soil and root rot.
- Moisture balance. A larger soil volume stays wet longer. Matching volume to the plant’s water needs is the single most impactful care decision you can make.
- Soil budget. Knowing exact volume before you shop means zero waste. You buy one bag or three — not four bags with one left rotting behind the shed.
If you also grow in raised beds, our soil calculator for raised garden beds applies the same principle at larger scale. The rule is always: measure first, buy second.
How to Use the Pot Volume Calculator: 3-Step Method
Our plant pot volume calculator works for round pots, cylindrical nursery containers, tapered decorative planters, and fabric grow bags. Here is how to use it:
- Step 1 — Measure inside diameter. Stretch a tape measure across the opening from inner rim to inner rim. Never include the wall thickness.
- Step 2 — Measure inside depth. Drop a ruler to the base and read to the rim. For fill volume, subtract 1.5 inches (4 cm) to leave proper headspace.
- Step 3 — Enter both values. Select your unit (inches or centimetres) and your output unit (gallons, litres, quarts, or cubic feet). The result appears instantly.
The advanced mode accepts a second diameter for tapered pots — enter the top diameter and the base diameter separately, and the calculator uses the truncated cone formula automatically.
Let's Calculate Plant Pot Volume Quickly!
Calculate exact pot volume for perfect plant growth. Determine soil capacity in gallons, liters, and cubic feet. Get accurate results for any container size with our free easy gardening calculator.
Calculate Pot Volume
Standard Plant Pot Sizes
| Pot Size | Diameter | Height | Gallons | Liters | Cubic Feet |
|---|---|---|---|---|---|
| 1 Gallon | 6.5 inches | 6.5 inches | 1 gal | 3.8 L | 0.13 cu ft |
| 2 Gallon | 8.5 inches | 7.5 inches | 2 gal | 7.6 L | 0.27 cu ft |
| 3 Gallon | 10 inches | 9 inches | 3 gal | 11.4 L | 0.40 cu ft |
| 5 Gallon | 12 inches | 10 inches | 5 gal | 18.9 L | 0.67 cu ft |
| 7 Gallon | 14 inches | 11 inches | 7 gal | 26.5 L | 0.94 cu ft |
| 10 Gallon | 16 inches | 13 inches | 10 gal | 37.9 L | 1.34 cu ft |
| 15 Gallon | 18 inches | 15 inches | 15 gal | 56.8 L | 2.00 cu ft |
| 20 Gallon | 22 inches | 17 inches | 20 gal | 75.7 L | 2.67 cu ft |
| 25 Gallon | 24 inches | 18 inches | 25 gal | 94.6 L | 3.34 cu ft |
| 30 Gallon | 26 inches | 20 inches | 30 gal | 113.6 L | 4.01 cu ft |
Plant Pot Volume Formulas
Round Pot (Cylindrical) Formula
Where:
- π (pi) = 3.14159
- Diameter = width across top of pot
- Radius = diameter divided by 2
- Height = depth from bottom to rim
Example: A pot with 12 inch diameter and 10 inch height:
Convert to gallons: 1,130.97 ÷ 231 = 4.90 gallons
Square Pot (Rectangular) Formula
Where:
- Length = longest side of pot
- Width = shortest side of pot
- Height = depth from bottom to rim
Example: A pot with 10 inch length, 10 inch width, and 8 inch height:
Convert to gallons: 800 ÷ 231 = 3.46 gallons
Tapered Pot Formula (Approximate)
Where:
- r₁ = top radius (diameter ÷ 2)
- r₂ = bottom radius
- Height = pot depth
Soil Volume Conversion Formulas
Disclaimer: This plant pot volume calculator provides estimates based on standard formulas. Actual pot capacity may vary due to taper, shape, and manufacturing differences. Nursery pot sizes use trade gallon measurements which differ from liquid gallons. For precise measurements, verify with water measurement method. This tool is for informational purposes only. Always check manufacturer specifications when available.
How to Calculate the Volume of a Pot by Hand: Formula and Worked Example
The volume of a pot formula is based on the cylinder. Here it is:
Volume = π × radius² × height
Step by step:
- Measure the inside diameter at the top. Divide by 2 to get the radius.
- Square the radius (multiply it by itself).
- Multiply by π (3.14159).
- Multiply the result by the inside depth (height) of the pot.
- This gives cubic inches (if you measured in inches) or cubic centimetres (if in cm).
- Divide cubic inches by 231 to get US gallons. Divide cubic centimetres by 1,000 to get litres.
Worked Example: 12-Inch Pot, 10 Inches Deep
- Inside diameter = 12 inches. Radius = 6 inches.
- π × 6² = 3.14159 × 36 = 113.1
- 113.1 × 10 (depth) = 1,131 cubic inches
- 1,131 ÷ 231 = 4.9 gallons
So that standard 12-inch pot holds just under 5 gallons of potting mix. For metric: the same pot in centimetres (30.5 cm diameter, 25.4 cm deep) gives 18.5 litres.
Tapered Pot Formula (Truncated Cone)
Most decorative planters are wider at the top than the base. Use the truncated cone formula:
Volume = (π ÷ 3) × height × (R¹² + R¹×R² + R²²)
Where R¹ is the top inside radius and R² is the base inside radius. The calculator handles this automatically in advanced mode. Our companion planter volume guide walks through the tapered formula in detail for window boxes and large decorative containers.
🪴 Pot Size Chart
Convert standard nursery container diameters to gallon and liter capacities instantly
Below is the definitive reference chart for standard round nursery pots. Product estimates assume a container depth roughly equal to its top diameter, which matches most traditional commercial nursery layouts.
| Pot Diameter | US Gallon Capacity | Metric Volume | Typical Application Tiers |
|---|---|---|---|
| 6 inch | ~0.25 gal (1 Quart) | 0.95 L | Standard seedling starter profiles & cutting roots |
| 8 inch | ~1 gal | 3.8 L | Small herbs, annual flushes, or early repots |
| 10 inch | 2 – 3 gal | 7.5 – 11 L | Varies by depth: shallow bowls run 2 gal; deep configurations run 3 gal |
| 11 inch | ~3 gal | 11.4 L | Mid-sized houseplants & vegetable variants |
| 12 inch | 3 – 5 gal | 11 – 19 L | Standard container crop setups; standard pro units hover at 4–5 gal |
| 13 inch | ~5 gal | 19 L | Robust vegetable roots & compact ornamental arrangements |
| 14 inch | 5 – 7 gal | 19 – 26 L | Most common operational standard for small shrubs & perennials |
| 15 inch | ~7 gal | 26 L | Perennial specimen management & deep container sets |
| 16 inch | 7 – 10 gal | 26 – 38 L | Commercial trade configurations standardly sold as #7 or #10 pots |
| 17 inch | ~10 gal | 37.9 L | Small ornamental trees & expansive broad-root crops |
| 19 inch | 12 – 15 gal | 45 – 57 L | Substantial home garden focal features & small fruiting trees |
| 20 inch | ~15 gal | 56.8 L | Large scale landscaping pots, small trees & specimen shrubs |
| 22 inch | 20 – 25 gal | 76 – 95 L | Dwarf fruit trees, patio citrus varieties & massive tropical statement items |
| 24 inch | 25 – 30 gal | 95 – 114 L | Maximum-tier commercial home containers & permanent landscaping trees |
How many true gallons does a #7 pot hold?
Quick answer: A #7 trade-size nursery pot holds approximately 5.5 to 6 true US gallons of soil, not 7.
The full trade-size reference:
- #1 pot: 0.8 true gallons (not 1)
- #2 pot: 1.6 true gallons (not 2)
- #3 pot: 2.5 to 2.8 true gallons (not 3)
- #5 pot: 3.8 to 4.5 true gallons (not 5)
- #7 pot: 5.5 to 6.0 true gallons (not 7)
- #10 pot: 7.5 to 8.5 true gallons (not 10)
- #15 pot: 11 to 13 true gallons (not 15)
- #25 pot: 18 to 22 true gallons (not 25)
Fabric smart pots and grow bags follow the same convention. A “10 gallon grow bag” typically holds 7.5 to 8.5 gallons of soil by true measure. The smart pot calculator mode in our tool applies the trade-size correction automatically when you select a named grow bag size.
🪴 Metric Nursery Pot Volumes
Convert metric container diameters to exact liter capacities for global gardening standards
Gardeners in the UK, Europe, and Australia primarily work in centimetres and litres. Below is the reference breakdown for the most commonly searched metric pot profiles.
| Pot Sizing Standard | Average Native Depth | Litre Capacity | US Gallon Match |
|---|---|---|---|
| 14 cm pot | 9 – 12 cm | 1.0 – 1.8 L (Avg: 1.54 L) | ~0.4 gal |
| 15 cm pot | ~12 cm | ~2.1 L | ~0.55 gal |
| 6 inch (15 cm) pot | ~12 cm | 0.8 – 1.2 L | ~0.25 gal (1 Quart) |
| 8 inch (20 cm) pot | ~18 cm | ~5.7 L | ~1.5 gal |
• DE / AT / CH: Voller Support für zentimeterbasierte Eingaben (Blumentopf Volumen berechnen, Topfvolumen berechnen, Topf volumen berechnen, Blumentopf liter berechnen, liter berechnen topf).
• NL / BE: Ondersteuning voor inhoud bloempot berekenen en liter potgrond berekenen.
• EE / RU: Полная поддержка для запросов "объем горшка калькулятор" с выводом в литрах.
📏 How to Measure a Plant Pot
Get accurate measurements for your soil calculations and potting configurations
| Pot Type / Sizing Query | True Dimensional Breakdown | Standard Volume Capacity |
|---|---|---|
| How to measure a flower pot? | Measure the inside diameter across the top opening (inner rim to inner rim) and the inside depth from the floor to the top lip line. | Always rely exclusively on internal tracking metrics for volume mapping. |
| Sizing in inches meaning? | Plant pot sizes in inches refer strictly to the top inside diameter. | A standard 10-inch pot measures exactly 10 inches across the interior rim opening. |
| 1 Quart plant pot | 4 inches (10 cm) Top Diameter × 3.5 inches (9 cm) Inside Depth | ~0.95 Liters / 1 US Quart |
| 10 Gallon pot | ~16 inches (41 cm) Top Diameter × 12 to 14 inches (30–36 cm) Depth | Standard #10 Trade Size Volume |
| 30 Gallon pot | ~20 inches (51 cm) Top Diameter × 18 inches (46 cm) Depth | Heavy operational nursery stock profile |
Grow Bag and Smart Pot Volume Calculator
Fabric grow bags air-prune roots and improve drainage, which is why they are increasingly popular with tomato growers and cannabis cultivators alike. Calculating their volume uses the same cylinder formula, but two factors change the real fill volume:
- Fabric bags bulge when filled. The actual diameter is slightly larger than the manufacturer’s stated size, adding small volume.
- Trade sizing applies. A “7 gallon” smart pot holds 5.5–6 true gallons of soil.
What is the volume of a 15 gallon grow bag in cubic feet?
Quick answer: 15 gallons ÷ 7.48 = 2.0 cubic feet. So a 2 cubic foot bag of potting mix fills one 15-gallon grow bag almost exactly.
How many litres is a 7 gallon grow bag?
Quick answer: 7 gallons × 3.785 = 26.5 litres labelled volume. True fill volume is closer to 20–23 litres after trade-size correction.
The smart pot calculator mode in our tool lets you select a named grow bag size and returns the true soil volume you should purchase, with trade-size correction built in.
Matching Pot Volume to Your Plant: A Size Guide
Now that you can calculate and convert any pot volume, how do you decide which size to use? The right volume matches the plant’s root mass — not its canopy. A good rule of thumb is to repot into a container only 1 to 2 inches larger in diameter than the current pot.
Guidelines from the Royal Horticultural Society and University of Minnesota Extension:
- Seedlings and cuttings: 4 to 6 inch pots (1 quart to 1 gallon / 0.95–3.8 litres)
- Small herbs and compact houseplants: 6 to 8 inch pots (1 to 2 gallons / 3.8–7.6 litres)
- Medium tropicals and vegetables: 10 to 14 inch pots (2 to 7 gallons / 7.6–26.5 litres)
- Tomatoes, peppers, cucumbers: 5 to 15 gallon containers (18.9–56.8 litres)
- Dwarf fruit trees, large shrubs: 15 to 30 gallon containers (56.8–113.6 litres)
- Large specimen and landscape trees: 25 gallon and above
Plant-Specific Pot Volume Recommendations
Orchids. Orchids want airflow around roots, not just volume. After calculating your container’s volume, use our orchid potting mix calculator to blend the right bark, perlite, and sphagnum ratio for that exact volume.
Tomatoes and food crops. Heavy feeders need at least 5 gallons, ideally 10 to 15. If you are planning a productive container garden, our fruits and garden grow calculator combines pot sizing, plant spacing, and harvest projections in one place.
Monstera and large tropicals. Young Monstera fits in a 10-inch pot. Mature specimens need 14 to 20 inches. For repotting timing and root-bound diagnosis, our Monstera deliciosa care guide explains exactly when to size up.
Alocasia. Alocasias manage dormancy in proportion to pot volume — too large a pot during dormancy causes rot. Our Alocasia zebrina dormancy guide covers pot size management through the dormant cycle.
Drought-resistant plants. Xeriscape container plants perform better in smaller, well-drained volumes. Our drought-resistant garden calculator recommends pot sizes alongside plant and soil selections.
Low-maintenance houseplants. Not sure which plants suit your pot size and lifestyle? Our long-life plants selector matches you with durable species by container size and light level. Our guide to moody houseplants for beginners covers 25 statement varieties that thrive in 3 to 7 gallon mid-size containers.
All indoor plants. For a complete care system tied to your pot size — watering schedules, fertiliser, light levels — our indoor plant care calculator is the natural companion tool to this volume guide.
🪴 Pot Volume Calculator FAQs
How many gallons is a 12x12 pot?
How many gallons is a 10-in pot?
How many gallons is an 8 inch nursery pot?
What is pot size in litres for a 14 cm nursery pot?
What is the volume of a 15 cm pot in litres?
What size is a 14 cm plant pot in litres?
How many cubic feet is a 15 gallon pot?
How many cubic feet is a 20 gallon pot?
How many cubic feet is a 3 gallon pot?
How many quarts is my pot?
What is the volume of a 6-inch nursery pot in quarts?
How do I calculate how many litres of potting mix my container needs?
How many litres of soil does a 10 gallon pot need?
What is the best estimate for the volume of a small pot?
How do I tell how many gallons a pot is without measuring?
How many gallons is my pot?
How do I use a pot volume calculator for cooking pots?
What is the volume of a 1/4 inch deep layer in a 6 inch diameter pot?
What soil type should I use once I know my pot volume?
How many plants fit in my garden space after I have sized my pots?
Your Complete Pot Volume Reference
Here is the complete picture in one place:
- Use the pot volume calculator above to get exact results for any container shape in gallons, litres, quarts, or cubic feet.
- Use the pot size chart in Section 4 for instant answers by diameter (6 inch through 24 inch).
- Use the conversion tables in Section 5 to convert between gallons, litres, cubic feet, and quarts for any pot size.
- Use the fill guide in Section 6 to calculate how much potting mix to buy, with headspace accounted for.
- Refer to Section 7 for trade-size corrections on nursery containers and smart pots.
- Use Section 8 for metric nursery pot volumes (14 cm, 15 cm, 8 inch, and international language equivalents).
Whether you are working out how many gallons is a 16 inch pot, converting a 10 gallon pot to litres, figuring out how many 5 gallon pots a 2 cubic foot bag will fill, or identifying your 14 cm nursery pot volume in litres — every answer is on this page.
Next steps: head to the soil calculator for pots to convert your volume into a shopping list, or use the gallon pot size finder to work backwards from gallon size to diameter. Happy growing.
