Enter your greenhouse area, crop type, season, and irrigation method to instantly calculate daily water demand, weekly totals, and the storage tank size you need on hand.
Enter your greenhouse details to get precise irrigation water requirements
Greenhouse area
Growing Area
Storage Days
days
Crop & season
Crop Type
Season / Climate
Irrigation method & custom rate
Irrigation Type
Measured Crop Uptake (optional)
L/m²/day
If you know what the crop actually uses (supply minus drain, or from a weighing gutter), enter it here. It replaces the crop and season estimate; irrigation losses are still added.
Optional checks optional
Drain to Waste
% of supply
Used only for "Substrate drip + drain" (run to waste). Enter the drain % you aim for (from your drain meter); blank uses 20%.
Number of Plants
plants
Shows litres per plant per day, the easiest number to check against your drippers.
⚠ Please enter a valid growing area greater than zero.
WaterTankCalculator.com — Greenhouse Water Usage Results
Your Results
Daily Water Requirement
—
Litres per Day
Daily (US Gallons)
— gal/day
Weekly Total
— L/week
Weekly (US Gallons)
— gal/week
Monthly Estimate
— L/month
Rate Applied
— L/m²/day
Recommended Tank
— litres
Crop Uptake
— L/m²/day
Per Plant
— L/day
Suggested Tank to Buy
— litres
Irrigation Overview
📖 How To Use
How to Use This Greenhouse Water Usage Calculator
Getting an accurate greenhouse irrigation estimate takes less than a minute. Follow these steps:
Enter your greenhouse growing area
Measure the total floor area where plants are growing — not the external footprint. Choose from square metres, square feet, hectares, or acres. Only count the area that receives irrigation, not paths or equipment zones.
Select your crop type
Each crop has a different daily water use. Tall fruiting crops such as tomatoes and cucumbers are high consumers; lettuce and herbs need far less. The built-in rates are for a mature crop in a ventilated greenhouse — young plants use much less. If you grow multiple crops, run the calculator separately for each zone and add the results.
Choose season and irrigation method
Greenhouse water use follows sunlight more than anything else, so summer days need far more than winter ones. Pick your irrigation method: drip in soil, drip in substrate with drain to waste, sprinklers, flood, or recirculating hydroponics. The calculator adds the right losses for each.
Set your storage buffer (days)
Enter how many days of water you want to keep in reserve. For a reliable supply, most growers keep 3–7 days on hand. The recommended tank size will be calculated from this value.
Review and copy your results
Results show daily litres and gallons, weekly and monthly totals, crop uptake, litres per plant if you entered a plant count, and the storage you need — plus a suggested tank to buy with a 15% margin. Use the copy button to save results for purchasing, planning, or reporting.
Tip: The best number is your own. If you grow in substrate, daily supply minus daily drain is what the crop actually used — enter that in Measured Crop Uptake on a sunny day in your peak month and the tank size will match your greenhouse, not an average one. Always check substrate or soil moisture before changing schedules.
📐 The Formula
Greenhouse Water Usage Formula Explained
The calculation follows standard crop evapotranspiration (ET) methodology adapted for enclosed greenhouse growing:
Daily Water Need (L) = Area (m²) × Crop Rate (L/m²/day) × Season Factor ÷ Irrigation Efficiency
Substrate run-to-waste: ÷ (1 − Drain fraction) instead of ÷ Efficiency
Weekly Total = Daily Need × 7
Tank Size (L) = Daily Need × Storage Days Required
Tank to Buy = Tank Size × 1.15, rounded up to a typical size
The crop ET rate is the baseline water use per square metre per day. The season factor adjusts for temperature and solar radiation. The irrigation efficiency accounts for method-specific losses. FAO uses 90% for drip, 75% for sprinklers and 60% for surface irrigation as typical figures; recirculating hydroponics loses very little because unused solution returns to the tank.
Two things make greenhouses different from open fields. First, the cover cuts sunlight and wind, so evaporative demand inside is lower — a field study in unheated plastic greenhouses in Almería, Spain measured it at 30–40% below outdoors. Second, substrate growers deliberately apply extra water so that some drains out of the slab and carries salts with it. That drain is a real water cost unless it is recirculated, so the calculator handles it separately.
Crop Water Rates (L/m²/day) — Baseline Values
Crop
Low Estimate
Mid (Used)
High Estimate
Growth Stage
Tomatoes
3.5
4.5
6.0
Fruiting peak
Cucumbers
4.0
5.0
6.5
Fruiting peak
Lettuce / Leafy
1.5
2.0
3.0
Mid-growth
Peppers
2.5
3.5
5.0
Fruiting
Herbs
1.0
1.8
2.5
Established
Strawberries
2.0
2.8
4.0
Fruiting
Flowers / Ornamentals
2.0
3.0
4.0
Flowering
Cannabis / Hemp
3.0
4.0
5.5
Vegetative
Seedlings
0.8
1.2
1.8
Germination
These are planning values for crop uptake (1 L/m² = 1 mm of water) of a mature crop at spring conditions, not fixed constants. As a check, UF/IFAS Extension puts a full-grown greenhouse tomato at 1.5–2 quarts (1.4–1.9 L) per plant on a sunny day, which at 2.5–3 plants/m² is about 3.5–5.7 L/m²; in the Almería study, average daily use across melon, bean, pepper and watermelon crops ranged from 0.3 to 4.5 L/m². Your own drain measurements will always beat a table.
Season & Irrigation Efficiency Multipliers
Factor
Value
Explanation
Summer
× 1.25
Higher temperatures, more transpiration
Spring
× 1.00
Baseline growing conditions
Autumn
× 0.85
Reduced light and cooler air
Winter
× 0.65
Low light, minimal transpiration
Tropical
× 1.30
Year-round heat and humidity
Drip in soil
÷ 0.90
FAO typical drip efficiency
Drip in substrate
÷ (1 − drain)
Drain to waste, e.g. 20% drain → ÷ 0.80
Sprinkler Efficiency
÷ 0.75
FAO typical; evaporation and drift
Flood / Furrow
÷ 0.60
40% loss through runoff and deep percolation
NFT / Hydroponics
÷ 0.98
Near-perfect recirculation efficiency
Fogger / Mist
÷ 0.85
Moderate losses to air evaporation
Season factors are planning multipliers that reflect how much more light and heat a greenhouse gets in summer than in spring; they are estimates, not measured constants. Fogging for humidity or cooling uses extra water on top of irrigation, which this calculator does not include.
🌱 When to Use This
Greenhouse Irrigation Sizing Use Cases
Sizing a New Greenhouse Water Supply
Before installing a bore, rainwater harvesting system, or mains connection, you need to know your peak daily demand. Use this calculator with your largest crop and hottest season to size the supply correctly. The suggested tank already includes a 15% margin; add more if your water source is unreliable.
Specifying a Storage Tank
Greenhouses often rely on stored water to bridge gaps in supply or to buffer against peak-demand periods. Enter your daily usage and set the storage days field to 3–5 for a normal buffer, or 7–14 days for off-grid or drought-prone setups. The recommended tank output tells you the minimum vessel size to purchase.
Irrigation Schedule Planning
Knowing your precise daily volume allows you to set irrigation controller run times accurately. Divide daily litres per plant by your dripper flow rate (L/hour) to get total run time per day. In soil, that is usually split into a few longer cycles; in substrate it is given as many short pulses through the day (see the FAQ below).
Rainwater Harvesting Feasibility
Compare your monthly water need (from this calculator) against your expected monthly roof catchment. If catchment exceeds usage, rainwater harvesting alone can supply your greenhouse. Use our Rainwater Harvesting Calculator alongside this tool for a complete picture.
Commercial & Research Greenhouses
For multi-bay or research greenhouses with varied crop zones, run the calculator separately for each zone at its own crop type and density. Sum all daily totals to size a shared header tank or mains connection for the entire facility.
🧮 Worked Example
Worked Example: 1,000 m² of Substrate Tomatoes in Summer
A grower has 1,000 m² of tomatoes in grow bags at 2.7 plants/m² (2,700 plants), watered by drip with a 20% drain target, and wants 3 days of storage.
Step
Working
Result
Crop uptake
4.5 L/m² × 1.25 (summer)
5.63 L/m²/day
Supply with 20% drain
5.63 ÷ (1 − 0.20)
7.03 L/m²/day
Daily supply
7.03 × 1,000 m²
7,031 L/day
Per plant
7,031 ÷ 2,700
2.6 L supplied, 2.1 L used
Storage
7,031 × 3 days
21,094 L
Tank to buy
21,094 × 1.15, rounded up
25,000 L (≈ 6,600 US gal)
The 2.1 L a plant uses is just above the 1.4–1.9 L UF/IFAS gives for a full-grown tomato on a sunny day, so it is a slightly conservative design figure — which is what you want for a tank. The same crop in soil with drip at 90% would need 6,250 L/day. If the drain were collected and recirculated, supply would fall back toward the 5,625 L the crop actually uses.
❓ FAQ
Frequently Asked Questions
How much water does a greenhouse use per day?
It depends heavily on crop type, area, and season. A small hobby greenhouse of 20 m² growing mature tomatoes on drip in summer uses about 125 litres per day. A 500 m² lettuce greenhouse in spring on drip uses about 1,100 litres a day. In winter they use roughly two-thirds of the spring figure, and less again where days are very short. This calculator accounts for all variables to give you a number specific to your situation.
How do I calculate greenhouse water requirements manually?
Multiply your growing area (in m²) by the crop's daily water use (L/m²/day), then apply a season multiplier and divide by your irrigation system's efficiency. For example: 100 m² of tomatoes × 4.5 L/m²/day × 1.25 (summer) ÷ 0.90 (drip in soil) = 625 litres per day. For substrate with drain to waste, divide by (1 − drain fraction) instead — with 20% drain, by 0.80.
What size water tank do I need for my greenhouse?
Most growers hold 3–7 days of water in reserve, based on how long their supply could be interrupted. Multiply your peak daily water requirement by the number of days. For 500 L/day with a 5-day buffer, you need 2,500 litres of storage, so buy about a 3,000-litre tank once you add a 15% margin for the water below the outlet. For off-grid or areas with unreliable supply, budget for 10–14 days.
Which irrigation method uses the least water in a greenhouse?
NFT (Nutrient Film Technique) and other recirculating hydroponic systems use the least, because unused solution returns to the reservoir — the calculator uses 98%. Drip in soil is the most efficient soil-based method; FAO uses 90% as a typical figure. Substrate growing that runs to waste loses whatever drains out, often 20% or more of supply, unless the drain is collected and reused. Overhead sprinklers lose about a quarter to evaporation and drift, and flood irrigation can lose 40% or more.
How does season affect greenhouse water usage?
Sunlight is the main driver of greenhouse water use, with temperature and humidity next. This calculator uses planning factors of 1.25 for summer and 0.65 for winter relative to spring, so a greenhouse using 1,000 L/day in spring would need about 1,250 L/day in summer and 650 L/day in winter. Real swings can be bigger, especially in northern winters with very short days. Always design your supply and tank for peak summer demand.
Can I use rainwater for my greenhouse irrigation?
Yes — rainwater is generally ideal for greenhouse irrigation. It is naturally soft, free of chlorine and fluoride, and at ambient temperature (avoiding the root shock that cold mains water can cause). Use our Rainwater Harvesting Calculator to check if your roof catchment area can meet your daily demand.
How often should I water plants in a greenhouse?
Most greenhouse crops benefit from multiple short irrigation cycles per day rather than one long session. In substrate, UF/IFAS suggests about 4 ounces (120 mL) per plant per irrigation, so a full-grown tomato using 1.5–2 quarts on a sunny day gets roughly 12–16 short pulses; in soil, fewer and longer cycles are normal. Lettuce under NFT runs continuously. Always irrigate based on substrate or soil moisture and drain readings, not a fixed clock schedule. The total daily volume from this calculator should be distributed across your chosen number of cycles.
✅ Sources & Review
Sources and review
The efficiencies and the checks on the crop water rates on this page come from these references:
UF/IFAS Extension Bulletin 327 — Hochmuth & Hochmuth, Design Suggestions and Greenhouse Management for Vegetable Production in Perlite and Rockwool Media in Florida. A full-grown tomato uses 1.5–2 quarts per plant on a sunny day; about 4 ounces per irrigation.
Orgaz, Fernández, Bonachela, Gallardo & Fereres (2005) — Evapotranspiration of horticultural crops in an unheated plastic greenhouse, Agricultural Water Management 72. Evaporative demand 30–40% below outdoors; average daily ET 0.3–4.5 mm; seasonal ET 170–371 mm.
The crop rates and season factors are planning estimates reviewed against the figures above, not values taken from a single standard. The 20% default drain and the 15% purchase margin are typical grower and engineering practice. For the best result, enter your own measured uptake.
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.
