Enter your field area, emitter flow rate, daily irrigation hours, and buffer days to instantly calculate the correct storage tank capacity for your drip irrigation system.
Enter your system parameters — the calculator sizes your storage tank instantly
Field & Crop Parameters
Crop Type optional
Picking a crop fills in a typical emitter layout and a peak-summer run time (FAO-56 Kc mid, ETo 6 mm/day, 90% drip efficiency). If you enter the field area first, it also estimates the plant count. You can change any value afterwards.
Field Area for depth check
Plants / Trees
plants
Emitter & Irrigation Settings
Flow / Emitter
Emitters / Plant
nos
Hours / Day
hrs
Zones (one at a time)
zones
Buffer / Storage Days
3 days
1 day4 days7 days14 days
⚠ Please enter valid values (greater than zero) for all required fields.
WaterTankCalculator.com — Drip Irrigation Tank Size Results
Your Tank Size Results
Minimum Storage Needed
—
Litres (L)
Cubic Metres
— m³
US Gallons
— gal
UK Gallons
— gal
Daily Usage
— L/day
Total Emitters
— nos
Buffer Days
— days
Total Flow Rate
— L/hr
Water Weight
— kg
Suggested Tank to Buy
— L
Supply Flow Needed
— L/hr
Pump Run Time
— hrs/day
Water per Plant
— L/day
Tank Capacity Visual
📖 How To Use
How to Use This Drip Irrigation Tank Size Calculator
Sizing your irrigation storage tank correctly takes just a few measurements from your field. Here's how:
Enter your field area and plant count
Count the total number of plants or trees that will be on drip — plant count drives the emitter total. Field area is optional, but enter it: the calculator uses it to check whether your schedule puts on a sensible depth of water, and with a crop preset it estimates the plant count from the spacing.
Set the emitter flow rate and emitters per plant
Check your drip emitter specifications — most standard emitters are 2, 4, or 8 litres per hour. Enter how many emitters are placed at each plant (commonly 1–4 for fruit trees, 1–2 for vegetables).
Enter your daily irrigation hours
How many hours does each emitter run per day at peak season? This should come from the crop's water use, not habit — vegetables on 2 L/hr drippers in summer often need only 2–4 hours. If you water the field in zones one after another, enter the number of zones; the tank size stays the same but the pump flow drops and the pump runs longer.
Set buffer storage days
Use the slider to choose how many days of reserve you want stored — in case of pump failure, power outage, or supply interruption. Use 1–2 days on a reliable supply, 3–5 days on a single borehole pump, and 7 days or more where power or deliveries are irregular.
Read your results
The calculator shows the minimum storage in litres, gallons, and cubic metres, then a suggested tank to buy: the minimum plus 15%, rounded up to a typical tank size. The margin covers the water below the outlet that you can't use and keeps the tank from being run dry.
Pro Tip: Always round up, never down. A 4,800-litre minimum becomes 5,520 litres with the 15% margin, so buy a 6,000-litre tank rather than a 5,000. Running a drip system dry pulls air and settled sediment into the lines, which blocks emitters and stresses the crop.
📐 The Formula
Drip Irrigation Tank Size Formula Explained
The calculation follows a straightforward three-step logic used by irrigation engineers worldwide:
Step 1 — Total Emitters:
Total Emitters = Number of Plants × Emitters per Plant
Step 2 — Daily Water Demand (litres/day):
Daily Demand = Total Emitters × Flow Rate (L/hr) × Hours per Day
Step 3 — Tank Size (litres):
Tank Size = Daily Demand × Buffer Days
Step 4 — Tank to Buy:
Tank Size × 1.15, rounded up to a standard size
Check — Applied Depth (mm/day):
Depth = Daily Demand (L) ÷ Field Area (m²)
All emitter flow rates entered in gallons/hour are converted to litres/hour (× 3.785) before the calculation. One litre spread over one square metre is a 1 mm layer of water, which is why the depth check is so simple — and why it lines up directly with crop water use (ETc), which FAO-56 publishes in mm/day. The result is then converted to cubic metres (÷ 1,000), US gallons (÷ 3.785), and UK gallons (÷ 4.546) automatically.
Crop Water Requirement Reference
Crop
Area per Plant
Kc mid
Peak L / Plant / Day
Example Layout
Run Time
Tomato
0.75 m²
1.15
5.8 L
1 × 2 L/hr
2.9 hrs
Bell pepper
0.6 m²
1.05
4.2 L
1 × 2 L/hr
2.1 hrs
Strawberry
0.25 m²
0.85
1.4 L
1 × 1 L/hr
1.4 hrs
Table grapes
4.5 m²
0.85
26 L
2 × 4 L/hr
3.2 hrs
Citrus (mature)
24 m²
0.65
104 L
4 × 8 L/hr
3.3 hrs
Avocado (mature)
48 m²
0.85
272 L
6 × 8 L/hr
5.7 hrs
Sugarcane
1.5 m² per m of row
1.25
12.5 L per m of row
Dripline, 4 L/hr per m
3.1 hrs
Peak L/plant/day = area per plant × Kc mid × ETo ÷ drip efficiency, using ETo = 6 mm/day (a hot, dry summer), Kc mid from FAO-56 Table 12 and 90% drip efficiency from FAO Irrigation Scheduling Manual No. 4. Young trees, cooler months and partial canopies need much less. Scale linearly with your own ETo — at 4 mm/day, multiply by 0.67. For a stage-by-stage figure, use the Crop Water Need Calculator.
Checking Your Schedule Against Crop Water Use
The most common mistake we see in drip tank sizing is not the formula — it is the run time. A schedule copied from a neighbour or an old controller can easily put on two or three times the water the crop uses, and the tank gets sized for water that drains below the roots. Convert your daily volume to a depth and compare it with crop water use:
Depth (mm/day) = Daily Demand (L) ÷ Field Area (m²)
Crop need (mm/day) = Kc × ETo ÷ drip efficiency
At full canopy in a hot summer, most crops need about 4–9 mm/day from a drip system. Above about 12 mm/day you are past the peak water use of almost any crop. Orchards and widely spaced crops will read lower over the whole field because the ground between trees isn't covered. The calculator runs this check for you when you enter the field area.
Unit Conversions Used
1 US gallon = 3.785 litres
1 UK/Imperial gallon = 4.546 litres
1 cubic metre (m³) = 1,000 litres
1 hectare = 10,000 m²
1 acre = 4,046.86 m²
🚜 When To Use This Calculator
Who Needs a Drip Irrigation Tank Size Calculator?
This tool is designed for anyone setting up or expanding a drip irrigation system that relies on stored water — whether from a borehole, rainwater harvest, or municipal fill:
🍅
Market Gardeners
Size holding tanks for vegetable beds, polytunnels, and raised rows where mains pressure is unavailable.
🌳
Fruit Orchards
Calculate tank requirements for citrus, mango, avocado, and stone fruit farms with multiple emitters per tree.
🌾
Row Crop Farmers
Size large tanks for drip-irrigated maize, sugarcane, cotton, and soybean on borehole or canal supplies.
🏡
Home Growers
Determine the right IBC or poly tank for a kitchen garden or backyard fruit trees fed from rainwater harvesting.
🌿
Greenhouse Operators
Plan headtank or fertigation tank sizes for controlled environment drip systems with precise flow requirements.
🔧
Irrigation Designers
Quickly verify storage requirements during system design without manual spreadsheet calculations.
Buffer days matter more than you think: Pick buffer days by how long your supply could realistically be down. A pump repair or a few days of power cuts is common on borehole farms, so 3–5 days is a sensible starting point there; 7 days or more where water is trucked in or power is irregular. A crop at peak demand can show stress within a day or two without water, especially on sandy soil.
🧮 Worked Example
Worked Example: Drip Tank for 1 Acre of Tomatoes
One acre (4,047 m²) of tomatoes on 1.5 m rows with plants every 0.5 m, a borehole that can be down for up to 3 days, and a peak summer ETo of 6 mm/day.
Step
Working
Result
Plants
4,047 m² ÷ 0.75 m² per plant
≈ 5,400 plants
Water per plant
0.75 m² × 1.15 × 6 mm ÷ 0.90
5.8 L/day
Run time
5.8 L ÷ (1 emitter × 2 L/hr)
≈ 3 hrs/day
Daily demand
5,400 × 1 × 2 L/hr × 3 hrs
32,400 L/day
Depth check
32,400 L ÷ 4,047 m²
8.0 mm/day ✓
Storage
32,400 L × 3 days
97,200 L
Tank to buy
97,200 × 1.15, rounded up
115,000 L (≈ 30,400 US gal)
All 5,400 emitters running together need 10,800 L/hr (about 48 US GPM). Split into 2 zones, the pump only has to deliver 5,400 L/hr (about 24 GPM), and it runs for 6 hours a day instead of 3. The tank is the same size either way — zones change the pump, not the storage.
Compare this with a schedule of 2 emitters at 4 L/hr for 8 hours, which is the kind of setting we often see copied between farms: that is 64 L per plant, 345,600 L a day and 85 mm/day of water on the field — more than ten times what the crop can use. The tank would come out at over a million litres for the same field.
❓ FAQ
Frequently Asked Questions
How do I calculate the tank size for drip irrigation?
Multiply the total number of emitters by the emitter flow rate (litres/hour) and by your daily irrigation hours to get daily water demand. Then multiply by the number of buffer days you want stored. For example, 500 emitters × 4 L/hr × 8 hours × 3 days = 48,000 litres minimum tank size.
What flow rate should I use for my drip emitters?
Check the manufacturer's label on your drip emitters. Common flow rates are 1, 2, 4, and 8 litres per hour (L/hr). Pressure-compensating emitters maintain their rated flow across a range of pressures (typically 1–3.5 bar). If your emitters are rated in gallons per hour (GPH), use the GPH option in this calculator — it converts automatically.
How many buffer days should I plan for?
For farms connected to a reliable mains or canal supply, 1–2 days is usually sufficient. For borehole-fed systems, 3–5 days is a common choice to cover pump repairs and power outages. For remote off-grid farms or areas with irregular supply, plan for 7–14 days. Larger buffer storage costs more upfront but protects crops worth far more.
Can this calculator be used for subsurface drip irrigation (SDI)?
Yes. Subsurface drip irrigation uses the same flow rates per emitter — the calculation logic is identical. Enter the total number of emitter points (outlets) in your SDI laterals as your emitter count, use the rated flow per emitter from the dripline specification, and proceed as normal.
How do I size a tank for drip irrigation on a 1-acre field?
It depends on your crop and plant spacing. For example, tomatoes at 1.5 m × 0.5 m spacing give about 5,400 plants on 1 acre. With 1 emitter of 2 L/hr per plant running 3 hours a day at peak: 5,400 × 1 × 2 × 3 = 32,400 litres per day, or 8 mm of water over the acre, which matches peak tomato water use in a hot summer. For 3 buffer days that is 97,200 litres, so buy a tank of about 115,000 litres with the 15% margin. Enter your actual numbers into this calculator for your own result.
What is the difference between a head tank and a fertigation tank in drip irrigation?
A head tank (or header tank) stores the bulk water supply and provides gravity pressure to the drip system. A fertigation tank is usually smaller and contains a concentrated fertiliser solution injected into the water flow. This calculator sizes the main water storage (head tank). Fertigation tanks are typically 100–2,000 litres and sized separately based on nutrient application rates.
How much pressure do I need in the tank for drip irrigation to work?
Standard non-compensating drip emitters require 0.5–1.5 bar (7–22 psi) of operating pressure. Pressure-compensating emitters work across 1.0–3.5 bar. Every 10 metres of height between the water level and the emitters gives about 0.98 bar (14.2 psi), before friction losses — a screen or disc filter and the pipework can take 0.2–0.5 bar of that. Most gravity-fed drip systems therefore need the tank well above the field, low-pressure emitters, or a pump. Use our Water Pressure Calculator to check whether your tank height delivers sufficient pressure.
Should I add extra capacity beyond the calculator result?
Yes — always add 10–15% to the calculated minimum. This covers the water below the outlet that you can't draw (dead storage), the space at the top above the overflow, and the practical reality that running a tank to zero draws settled sediment into the lines and blocks emitters. The calculator shows this as the "Suggested Tank to Buy". Round up to the next standard tank size available from your supplier.
✅ Sources & Review
Sources and review
The crop water figures, efficiency and conversion factors on this page come from these references:
FAO Irrigation and Drainage Paper No. 56 — Allen, Pereira, Raes & Smith (1998). ETc = Kc × ETo and the Table 12 Kc mid values used in the reference table and crop presets.
The 15% purchase margin and the standard-size rounding are engineering practice rather than a published standard; use your supplier's actual tank sizes when you order.
Reviewed by John Mac, PE, Water Systems Specialist
Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.
