Getting Started
What a rain barrel is, how it works, and whether it suits your roof and garden.
Grow a greener garden with rainwater from your roof
Catch roof rainwater in a barrel and water your garden, lawn and ornamental plants — free, soft water, straight from the sky.
Non-potable use only: ornamental garden and lawn watering. Not for drinking, cooking or bathing.
Rain Barrel Calculator
How much rainwater can your roof catch? Enter your roof size and rainfall.
Typical range 75–95%. Losses come from splashing, evaporation and gutter overflow.
Overflow is the storm water left over after your barrels are full.
Results
- Roof area
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- Gallons per inch of rain
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- Gallons per storm
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- Gallons per year
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- Barrels needed to catch one storm
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- Barrels filled by one storm
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- Overflow — water beyond your barrels
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Formula: gallons = roof area (sq ft) × rainfall (inches) × 0.623 × (efficiency ÷ 100). First flush, when on, deducts 10 gallons per 1,000 sq ft from each storm. The yearly total is before first-flush losses, since the number of storms per year varies. 1 gallon = 3.785 litres.
Estimates only — check local rules. Rainwater from this calculator is for non-potable, ornamental garden and lawn use only.
Start here
Setup & Install
Choosing a barrel, placing it, fitting a diverter and linking barrels together.
Troubleshooting
Slow flow, leaks, smells, algae and mosquitoes — fixes that actually work.
Equipment
Barrels, stands, diverters, filters, hoses and screens — what to buy and what to skip.
Latest guides
Rain Barrel Setup: Stand, Spigot, Overflow & Diverter Explained
A working rain barrel setup has four parts: a level stand, a spigot near the bottom, an overflow near the top, and a diverter in the downspout. Get those four right and a 55-gallon barrel will fill itself in the rain, give you water at the spigot with gravity pressure, and send the extra water […]
How to Install a Rain Barrel in a Weekend (Step-by-Step, Under $100)
You can install a rain barrel in one weekend afternoon for under $100, with basic hand tools and no plumbing experience. Pick a downspout, raise the barrel on a level stand, cut the downspout, fit a diverter, add spigot and overflow hose, then fill it and check for leaks. Plan on two to three hours, […]
Is Rainwater Safe for the Garden? What the CDC Actually Says
Rainwater from a barrel is fine for ornamental garden beds, shrubs, and lawns — but it is not safe to drink, and the CDC recommends tap or bottled water for watering plants you plan to eat. That one distinction, ornamental versus edible, is the whole answer. A barrel catches runoff from your roof, so the […]
How Many Rain Barrels Do I Need? (Roof Size + Rainfall Table)
For most homes, start with one 55-gallon barrel, and add a second if your roof is over 1,000 sq ft or you water ornamental beds often. One barrel catches the first 55 gallons of a storm; a 1,000 sq ft roof produces about 530 gallons from a single inch of rain, so even three linked […]
How Much Rainwater Can a 1,000 Sq Ft Roof Collect? (With Table)
A 1,000 square foot roof collects 623 gallons from 1 inch of rain before any losses, and about 530 gallons after a typical 85% collection efficiency. Over a year with 36 inches of rain, that same roof collects roughly 19,000 gallons after efficiency. The key number is 0.623: every inch of rain on every square […]
Rain Barrel Calculator: How Many Gallons Will Your Roof Collect?
A 1,000 square foot roof collects about 520 gallons from just 1 inch of rain, after an 85% collection efficiency and a 10-gallon first flush. That fills more than nine standard 55-gallon rain barrels from a single modest storm. The formula is simple: gallons = roof square feet × inches of rain × 0.623 × […]