Drip Irrigation Calculator
Design your drip irrigation system.
Enter number of plants, emitter flow rate, and water pressure to calculate system requirements and run time.
Drip irrigation flow calculation ensures your system delivers the right amount of water to each plant without over- or under-watering. The key is matching emitter flow rate and run time to your plants’ water requirements.
The Formula:
Run time (minutes) = Water per plant ÷ (Emitters per plant × Emitter flow rate) × 60
Total system flow (GPH) = Plants × Emitters per plant × Emitter flow rate
The emitters-per-plant term is the one people drop, and dropping it doubles or triples the run time. Two 1 GPH emitters on a tomato deliver a gallon in thirty minutes, not an hour.
Emitter Flow Rate Reference:
| Emitter | Flow rate | Typical use |
|---|---|---|
| 0.5 GPH (2 L/hour) | slowest | Herbs, flowers, sandy soil |
| 1.0 GPH (4 L/hour) | standard | Most vegetables |
| 2.0 GPH (8 L/hour) | fast | Shrubs, large containers |
| 4.0 GPH (15 L/hour) | fastest | Trees, 3 or 4 per tree |
Plant Water Requirement Reference (per plant, per day, mid-summer):
| Plant Type | Gallons | Liters |
|---|---|---|
| Herbs | 0.15–0.25 | 0.5–1 |
| Peppers | 0.4–0.5 | 1.5–2 |
| Tomatoes | 0.5–0.8 | 2–3 |
| Squash | 0.8–1.3 | 3–5 |
| Trees (established) | 3–10 | 10–40 |
Worked Example:
12 tomato plants, each needing 0.66 gallons a day. Using 0.5 GPH emitters, 2 per plant:
- Total emitters: 12 × 2 = 24
- Total system flow: 24 × 0.5 = 12 GPH
- Flow reaching each plant: 2 × 0.5 = 1 GPH
- Run time: 0.66 ÷ 1 × 60 = 40 minutes per day
- Water per session: 12 × 0.66 = 7.9 gallons (30 liters)
System Pressure:
Drip emitters want 15 to 30 PSI (1 to 2 bar). Fit a pressure regulator if your supply runs above that, which most municipal supplies do. Below 15 PSI the emitters deliver less than their rated flow, so every run time above comes out short without anything obviously going wrong.
Practical Tips:
- Run drip lines early morning. Evening watering leaves foliage damp overnight, which is how fungal disease gets started.
- Flush the lines monthly. Mineral deposits and algae build up at the far end of every run.
- Fit a 130-mesh filter ahead of any drip zone. A single grain of sand kills an emitter permanently.
- In clay, cut the flow rate rather than the run time. Clay accepts water slowly, and a fast emitter simply puddles and runs off.
- Long runs of thin tubing lose pressure along their length, so the last plant on a 100 ft run gets noticeably less than the first.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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