Free tool
Watering calculator
Pick your crop and tell us the bed size or how many pots you have — we'll estimate the litres of water needed each week, and how many 9-litre watering cans that is.
Sets the typical water need (low, medium or high).
Length × width of the bed or border in square metres.
Summer plants drink most; autumn least.
Drier areas like the East and South East need more; the wetter West and North less.
Water this bed needs each week
60 litres
≈ 7 cans (9-litre cans)
Assumptions
30 mm/week over 2 m² · high water need · Summer · Midlands
A guidance figure for UK gardens. Water deeply once or twice a week rather than a little every day — it draws roots down and builds drought resistance. Skip watering after decent rain, and always check the soil 5 cm down before reaching for the can. Containers dry out fastest and may need daily attention in a heatwave.
How to use it
Choose your crop from the list — each one carries a typical water need (low, medium or high) drawn from our UK grow data. Then pick whether you're watering open ground, where you enter the bed area in square metres, or containers, where you enter how many pots you have and roughly how many litres each holds. Set the season and tick the box if you're in the middle of a hot, dry spell. The results update as you change anything — no button to press. It's a handy starting point whether you're filling a water butt, planning a holiday watering rota, or just wondering how many trips to the tap a heatwave means.
How the calculation works
We start from a base of 10 mm a week for low-need crops, 20 mm for medium and 30 mm for high. That's scaled by season — summer is the full amount, spring is 0.7× and autumn 0.5× as plants slow and the weather cools — and a hot, dry week adds a further 30%. For open ground we use the simple fact that 1 mm of water over 1 m² is exactly 1 litre, so litres per week = mm × area. For containers we use a transparent rule of thumb: litres ≈ pots × (mm ÷ 10) × (litres per pot ÷ 10), so a 10-litre pot at 20 mm/week comes to about 2 litres. We then divide by 9 to show the equivalent in standard UK watering cans. Every figure is guidance — real needs swing with your soil, mulch, wind and the weather, so always check the soil before watering.
Frequently asked questions
- How much water do vegetables need each week?
- As a rough guide, a UK bed needs about 10–30 mm of water a week depending on the crop — thirsty plants like tomatoes, courgettes and runner beans want the most, while onions and garlic need least. Since 1 mm over 1 m² equals 1 litre, a 2 m² bed of medium-need veg in summer works out at roughly 40 litres a week. This calculator does the sum for your crop, area and season.
- Is it better to water a little every day or a lot less often?
- Less often but more deeply is almost always better for beds and borders. A good soak once or twice a week encourages roots to grow down in search of moisture, which makes plants far more drought-tolerant. Frequent shallow watering keeps roots near the surface where they dry out fast. Containers are the exception — they hold little soil and may need watering every day in hot weather.
- Do I still need to water after it rains?
- Often not. A steady soaking of rain can cover a week's worth of watering for an open bed, so check the soil 5 cm down before topping up — if it's damp, leave it. A brief summer shower, though, barely wets the surface and won't reach the roots, so treat light rain as if it never happened. Containers under leaves or a canopy can stay bone dry even in a downpour.