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
How to Winterize a Rain Barrel (Step-by-Step for Freezing Climates)
Winterize a rain barrel by draining it completely, disconnecting the diverter, restoring the downspout, and storing the barrel upside down before the first hard freeze. The whole job takes about 30 minutes, and it saves you from a cracked barrel in spring. A barrel left full through winter is one of the most common and […]
How Long Will a 55-Gallon Rain Barrel Last? (Watering-Days Calculator)
A full 55-gallon rain barrel lasts about one deep watering of a 200 square foot ornamental bed, or about two to three light waterings of the same bed. In days, that means one barrel lasts one to three days of regular watering in summer, depending on how big your beds are and how much water […]
How to Link Two Rain Barrels Together (Daisy-Chain Guide)
Linking two rain barrels together doubles your storage from 55 to 110 gallons, and it is the cheapest way to get more water without buying a bigger tank. Place the barrels side by side on level ground, connect them near the top with a short hose or pipe, and put the overflow on the last […]
Rain Barrel Overflow: Where Should It Go? (And 3 Mistakes to Avoid)
Rain barrel overflow should go at least 4 to 6 feet from your foundation, downhill, onto a lawn, an ornamental bed, a rain garden, or into a drain. That is the short answer, and it is the most important thing about a rain barrel system after the barrel itself. A barrel without a proper overflow […]
How to Keep Mosquitoes Out of a Rain Barrel (5 Methods That Work)
The most reliable way to keep mosquitoes out of a rain barrel is a fine mesh screen over every opening plus a tight-fitting lid that stays closed. Together they block adult mosquitoes from laying eggs in the water, and they work without chemicals, without cost, and without maintenance beyond a quick check after each storm. […]
First Flush Diverter: What Size Do You Need? (10 Gal per 1,000 Sq Ft Rule)
A first flush diverter should hold about 10 gallons for every 1,000 square feet of roof that drains into your barrel. That is the standard rule of thumb, and it is enough to send the dirtiest first water of a storm away from the barrel while keeping almost all of the storm for watering. For […]