Plant Watering Calculator
Calculate how much water a single plant or container needs per week.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Treat the output as a rough planning estimate. It does not account for rainfall, soil drainage, plant species, root depth, or local weather; check soil moisture and adjust to the plant and conditions.
Worked example
calculated with the default values below
Plant type Vegetable · Root spread diameter 1.5 ft · Number of plants 1 · Container volume (containers only) 5 gal · Sun exposure Full sun (1.2×) Water per plant per week 1.26 gal · Water per plant per week 4.78 L · Total for all plants 1.3 gal · Note Rough planning estimate only; rainfall, soil, species, root depth, and local weather can change water needs substantially
General background references
Disclaimer
These are general gardening estimates. Planting windows, growth, water and nutrient needs vary by place and plant. Check local extension guidance and product labels before acting on an estimate.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
G = max(0.3, π × (d ÷ 2)^2 × 0.62 × b × 12 × e)
- G
- Water per week (gal)
- d
- Canopy spread (ft)
- b
- Plant-type factor
- e
- Sun-exposure factor
Containers: G = pot gallons × 0.25 × e; b = 0.04–0.10, e = 0.7–1.4; litres = gal × 3.7854.
Frequently asked questions
How accurate is this watering estimate?
It is a rough planning estimate, not a watering prescription. Rainfall, soil, species, root depth, container drainage, and local weather can substantially change the amount needed; check soil moisture and adjust.