Calculator Inputs
Example Data Table
| Garden type | Area (m²) | Depth (mm/day) | Autonomy days | Efficiency (%) | Suggested tank (L) |
|---|---|---|---|---|---|
| Raised vegetable beds | 40 | 4 | 3 | 90 | 600 |
| Mixed flower garden | 85 | 5 | 4 | 85 | 2,500 |
| Warm-season lawn | 140 | 6 | 5 | 80 | 6,500 |
| Container and orchard mix | 220 | 5.5 | 5 | 82 | 9,000 |
Formula Used
Gross Daily Demand (L/day) = Area (m²) × Irrigation Depth (mm/day) × Plant Factor × Peak Multiplier
Net Daily Demand (L/day) = Gross Daily Demand ÷ Irrigation Efficiency
Usable Storage (L) = Net Daily Demand × Autonomy Days × (1 + Reserve Buffer)
Nominal Tank Volume (L) = Usable Storage ÷ Working Fill Fraction
Cylindrical tank: Diameter = 2 × √(Volume ÷ (π × Height))
Rectangular tank: Width = √(Volume ÷ (Height × Length/Width Ratio))
Rectangular tank: Length = Width × Length/Width Ratio
How to Use This Calculator
- Enter your irrigated garden area and choose the correct unit.
- Provide the average daily irrigation depth during active watering periods.
- Set autonomy days to show how long the tank should supply water without refill.
- Adjust plant factor for light, moderate, or high water demand planting.
- Increase the peak multiplier for hotter months or stronger evaporation conditions.
- Enter irrigation efficiency to account for spray loss, drift, or uneven delivery.
- Add a reserve buffer for safety and choose a practical working fill fraction.
- Select a tank shape and preferred height to estimate practical dimensions.
- Press the calculate button to view results, dimensions, and the Plotly chart.
- Use the CSV or PDF buttons to save the calculated design summary.
Frequently Asked Questions
1. What does autonomy days mean?
Autonomy days show how long the tank can cover watering without a refill. More days mean larger storage and better resilience during hot, dry spells.
2. Why is irrigation efficiency important?
Efficiency adjusts for losses from drift, evaporation, runoff, or uneven application. Lower efficiency means the tank must store more water to deliver the same root-zone moisture.
3. How do I choose plant factor?
Use lower values for drought-tolerant beds, around 1.0 for general mixed planting, and higher values for thirsty vegetables, containers, or dense summer growth.
4. What is the reserve buffer for?
Reserve buffer adds extra stored water beyond the basic calculated need. It helps cover pump issues, hotter days, scheduling changes, or short-term refill delays.
5. Why is nominal volume larger than usable storage?
A tank is rarely operated to the absolute brim or drained to zero. Working fill fraction keeps the design realistic and protects operating margin.
6. Should I choose cylindrical or rectangular tanks?
Cylindrical tanks are common and structurally efficient. Rectangular tanks can fit tighter spaces better, especially when wall alignment or site geometry matters.
7. Can I use this for rainwater storage planning?
Yes. This calculator sizes demand-side storage. You can compare the result with expected harvested rainwater supply to judge whether the tank volume is sufficient.
8. How much larger should I size a tank?
A modest step up to the next standard tank often improves reliability. It is especially helpful when demand spikes, refill intervals are uncertain, or expansion is likely.