Teaching · For Teachers · Earth science

A month of rain,
in barrels of
water.

Log what the rain gauge reads after each storm and measure the roof or bed it falls on. The calculator keeps the running total and turns millimeters or inches into liters or gallons, so a class can see what a month of weather adds up to.

Add up the rainWhat you get

The rainfall accumulation calculator

The worked example is made up: five April rains on a 4 by 3 meter garden shed roof with a 200 liter barrel. Nothing you type leaves this browser.

Loading the calculator. If nothing appears, turn on JavaScript.

What you get

Teaching · For TeachersFree

What you finish with
The total rainfall and the running accumulation, the water that fell on the catchment and the share collected, the barrels it fills and the biggest storm. It prints as a rain log and downloads as a spreadsheet.
Who it is for
Earth science students and teachers, school garden and environmental clubs, and families collecting rainwater.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Metric or US units. Up to 120 rain events. Prints a log; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The For Teachers space in Caveat Teaching.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Choose units and measure the catchment’s length and width from above.
  2. Set the share you expect to collect and, if you have one, the barrel size.
  3. Add each rain event from the gauge.
  4. Read the total, the water collected and the barrels filled.
  5. Print the log or download the spreadsheet.

Add up the rain

How rain becomes volume

Depth times surface.

The worked example: April on the shed roofApril rain62 mmfive events addedRoof12 m²4 m × 3 m, measured flatFell on the roof744 L62 × 12, 1 mm on 1 m² = 1 LCollected632.4 L85% reaches the barrelThe worked example: April on the shed roofApril rain62 mmfive events addedRoof12 m²4 m × 3 m, measured flatFell on the roof744 L62 × 12, 1 mm on 1 m² = 1 LCollected632.4 L85% reaches the barrel
One millimeter of rain on one square meter is exactly one liter, so rain depth times catchment size gives the water; gutters and splash lose a share of it.

The arithmetic

A rain gauge measures depth: how deep the rain would stand on flat ground if none ran off or soaked in. Depth times the size of the surface gives volume. In metric units this is tidy, since 1 millimeter on 1 square meter is exactly 1 liter. In US units, 1 inch on 1 square foot is 144 cubic inches, and a gallon is 231 cubic inches.

Measuring well

Set the gauge in the open, away from roofs and trees, and read it at the same time each day. Measure a sloped roof by its footprint from above, since rain falls vertically. Some water splashes out of gutters, wets the roof and evaporates; a share collected of 75 to 90 percent covers most roofs. Rules on collecting rainwater vary by place; check local guidance before installing a system.

Sources

  1. National Weather Service, Cooperative Observer Program and CoCoRaHS volunteer network: how to measure precipitation with a gauge (weather.gov; cocorahs.org).
  2. U.S. Environmental Protection Agency. Soak Up the Rain: rain barrels (epa.gov).
  3. U.S. Geological Survey, Water Science School: how much water falls during a storm (usgs.gov).
  4. NIST Handbook 44 and Special Publication 811: the U.S. gallon of 231 cubic inches and metric volume units.

The worked example is made up. Your rain log stays in this browser. Support: team@caveatacademic.com.