Garden calculator · Water
How many gallons is
an inch of water a week?
About 0.62 gallons per square foot.
A 4 × 8-foot bed takes roughly 20 gallons for one inch.
Work out your garden’s share
Enter the bed size and the depth you want to add. This converts water volume; it does not diagnose a plant’s needs.
For 32 square feet · 1 inch deep
102-gallon can fills
4.0hose minutes
Length × width × inches × 0.623
Volume before runoff or other losses. Source & calculation
What does “an inch of water” mean?
Picture an even, one-inch-deep layer spread across the area you are watering. A wider bed needs more gallons to make that same layer.
It is the amount you apply, not how far water travels into the soil. You do not need to leave an inch of standing water on the bed.
A ruler makes it real.
Put several straight-sided, level containers within the sprinkler’s reach. Measure the water inside them to see how much landed.
Illustration only. The screen drawing is not a physical ruler.
Measuring method: Iowa State University Extension.
Measure the way you water
Sprinkler: catch it in containers
Start with empty containers and note the run time. Compare the depths afterward. Big differences mean coverage needs adjusting before you trust one reading for the whole bed.
For example, ¼ inch in 15 minutes works out to about 60 minutes for an inch at the same rate. Retest if pressure, sprinkler position, or coverage changes. Pause if water runs off.
Hose or watering can: count gallons
Use the calculator above, then spread that volume slowly across the intended area. With a hose, time how long it takes to fill a known-volume bucket at your usual setting.
If a 2-gallon container fills in one minute, the flow is 2 gallons per minute. Delivering 20 gallons takes about 10 minutes, provided it soaks in instead of running away.
Bucket timing: University of Minnesota Extension.
Drip or soaker hose: check the soil
A container beside a drip line will not tell you how much reached the roots. Use emitter flow for a volume estimate, then check the soil’s wetting pattern and depth. A wet surface can hide dry soil underneath.
A starting point, not a rule for every plant
About an inch per week, including rain, is a common vegetable-garden starting point. Soil, weather, crop and growth stage change the schedule. Check moisture in the root zone before watering again.
- Seedlings & new transplants
- Small, shallow root systems need closer attention than established plants.
- Heat, wind & sandy soil
- Check more often. Faster drying may call for more frequent watering.
- Slow-draining or already-wet soil
- Do not force a weekly quota into saturated ground. Stop when water pools or runs off.
- Container vegetables
- Use the potting mix as your guide. Water when needed until excess drains, and empty the saucer. A bed-wide inch is not a pot-watering schedule.
Plant and soil differences: Iowa State. Container care: University of Maryland Extension.
Questions people ask
Does rain count toward the inch?
Yes. Use a rain gauge, then check that the rain reached the soil you are watering. Heavy runoff, a roof overhang or a dense canopy can make the gauge reading different from the water available to roots.
Can I just run my sprinkler for 30 minutes?
Only if you have measured what that setup delivers. Flow, pressure and coverage vary. A timed container test is more useful than a universal number of minutes.
Is an inch a week right for everything?
No. It is a useful starting point for many vegetable beds. Seedlings, pots, established drought-tolerant plants and poorly drained sites need different care. Use your plant’s guidance and check the soil.
How does the calculator get the gallons?
One square foot is 144 square inches. At one inch deep, that is 144 cubic inches of water. Divide by 231 cubic inches per US gallon: 0.623 gallons per square foot. Results are rounded to one decimal place.
Research you can follow
These publications support the methods above. The worked examples are calculations, not measurements from a farm trial.
Iowa State University ExtensionMeasuring sprinkler water, root-zone checks and vegetable needs
University of Minnesota ExtensionGallons for garden beds and timing a hose with a bucket
Oregon State University ExtensionThe inches-to-gallons conversion for garden area
University of Maryland ExtensionWhy container vegetables need their own watering checksPublications checked September 27, 2026. Explore the plant research library →