Nursery Pot Size Calculator

Enter plant and pot details

Choose a sizing method, then provide either rootball measurements or a target container volume. Optional fields help validate an existing pot.

How the calculator estimates pot capacity

• Rootball volume (if used) is modeled as a cylinder: V = π × (D/2)² × H.
• Target root-space scales rootball volume by stage, growth, and time multipliers.
• Gross pot capacity adjusts for freeboard and settling: V_gross = V_target / ((1−f)(1−s)).
• Existing pot volume uses a tapered model (frustum): V = (πH/3) × (R_t² + R_tR_b + R_b²).

Note: nursery containers vary by manufacturer; this tool provides practical sizing guidance, not a certified specification.

Steps for accurate recommendations

1. Measure the rootball diameter after removing the plant gently.
2. If possible, measure rootball height; otherwise leave it blank.
3. Select plant stage and growth rate to match expected vigor.
4. Set weeks until the next up‑potting, based on your schedule.
5. Adjust freeboard and settling if your mix shrinks a lot.
6. Click Calculate and compare the recommended trade size to your options.
7. If you already have a pot, fill the optional check fields.

Container sizing and root performance

Nursery containers influence drainage, oxygen, and rooting speed. When volume is too small, roots circle early and water swings between saturation and drought. Oversized pots can stay wet, slowing respiration and encouraging pathogens. This calculator balances capacity with practical headroom by estimating target root-space and then adding allowances for rim freeboard and media settling after irrigation cycles.

Nominal labels and real capacity

Nursery sizing often uses nominal trade gallons, while real capacity varies across brands and shapes. Two “3‑gallon” pots can differ by more than a quart because of taper, wall thickness, and height. The reference table provides typical top diameters and heights so you can compare physical fit. Use the dimensional checks to ensure the top opening clears the rootball comfortably. Measuring the top diameter with a ruler is a quick validation before you purchase trays or sleeves.

Tapered geometry and volume calculation

Tapered pots behave like a frustum rather than a perfect cylinder. Volume depends on both top and bottom diameters, so a wider base can add meaningful capacity without increasing height. The frustum formula captures this effect and converts cubic inches to gallons for easy interpretation. When you enter an existing pot, the tool estimates capacity and flags whether it meets your target requirement.

Transplant timing and growth factors

Transplant timing matters as much as size. Longer intervals between up‑potting demand extra volume so roots can expand without binding, while fast-growing crops typically need more headroom than slow growers. The stage and growth multipliers reflect typical root-to-shoot relationships, helping gardeners choose consistent steps. Adjust weeks until the next transplant to match your production schedule or seasonal constraints.

Watering strategy and media behavior

Selection should also consider watering habits and mix properties. Coarse media drains faster and tolerates larger pots, while fine mixes may require a tighter step to avoid persistent saturation. The freeboard setting keeps space for watering and mulch layers, and settling accounts for shrinkage after repeated soakings. After selecting a pot, verify drainage holes and avoid compacting the media. For heavy feeders, extra volume can stabilize moisture and temperature, improving nutrient uptake during hot afternoons.

FAQs

Sample inputs and typical outputs

These rows are illustrative; your results depend on freeboard, settling, and dimensional constraints.