Explaining water units to real people (who like basketball)

by Jay Lund

It’s March madness once again as we try to explain water conditions in California to real people in the midst of additional basketball madness.

We all enjoy and suffer with basketball.  This commonality can make it a useful unit of volume among the many units of volume used for water.

A basketball has the volume of about 1/4 cubic feet (4 basketballs per cubic foot).  So a flow of 1,000 cubic feet per second (cfs) has a volume equivalent of having 4,000 basketballs coming at you every second. 

An acre-foot (af) is a volume one foot deep over an acre of area.  It has a volume of 43,560 cubic feet or 325,850 gallons, or 174,240 basketballs.

One cfs flowing for one day (24 hours) discharges almost 2 acre-feet (1.98) of volume (348,480 basketballs/day).

A million gallons per day (mgd) has the same volume as 1.87 million basketballs per day. (There are 7.48 gallons per cubic foot)

A cubic meter (m3) is about 35.3 cubic feet, which equals about 141 basketballs of volume.

Here is a California water units translator (rounded some, highlighting the most useful conversions):

For California’s water infrastructure, the Sacramento Valley flood bypass system has a conveyance capacity of almost 750,000 cubic feet per second (600,000 cfs in the lower Yolo Bypass and 130,000 cfs in the Sacramento River main stem).  This is equivalent to the volume of 3 million basketballs per second (260,000 mega-basketballs per day – mbd).

California’s largest reservoir has a storage capacity of 4.55 million acre-feet, or almost 800 billion basketballs.

In terms of water use, most of California’s roughly 8 million acres of irrigated agriculture uses 3-4 acre-ft per acre annually (520,000-700,000 basketballs per acre/year) each year totaling about 26 million acre-ft per year, or 4.5 trillion basketballs of water per year.

California’s urban water users, almost 40 million people, use roughly 140 gallons per capita per day (74 basketballs/person-day or 27,100 basketballs/person-year), totaling about 7 million acre-ft per year, or 1.2 trillion basketballs of water per year of urban water use.

Maybe this basketball lens for California water use is helpful for “#SciComm” junkies and others at pains to communicate scienterrific things to real people.  As a civil engineering undergraduate student, it seemed that a third of all my calculations were unit conversions. We might have learned more with a single standard international unit such as basketballs (since metric hasn’t caught on much here).  (Still, if I made a mistake in the table, let me know.)

Welcome to March Madness!

About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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16 Responses to Explaining water units to real people (who like basketball)

  1. Maury D. Gaston says:

    I may well be wrong, but should the third paragraph be 250 balls instead of 1000?

  2. Tara Smith says:

    Very fun!

  3. Tim Moran says:

    Hi Jay – I’m not sure millions of basketballs is easier to picture than acre feet. And I keep wondering about the space between basketballs, since they are, um, round. Maybe I’m just a frustrated Golden State Warriors fan…

  4. chuck watson says:

    I was never that good at math but: if a baskeball has a volume of 4 cubic feet (which seems to me more like the volume of a beach ball) then wouldn’t a flow of 1000 cfs be equivalent to 250 basketballs per second – not 4,000?? Just wondering.

  5. Brian says:

    “A basketball has the volume of about 4 cubic feet. So a flow of 1,000 cubic feet per second (cfs) has a volume equivalent of having 4,000 basketballs coming at you every second. ”

    Wouldn’t that be 250 basketballs? A much less impressive visual. I like the b-ball comparison, though.

  6. Mike Hardesty says:

    As I remember 1 miner’s inch can be either 1/40 (11.25 gpm-Northern Calif) or 1/50 (9 gpm Southern Calif) of a second foot. Apparently, even in the past we, N vs. S Calif. couldn’t agree on this water matter?

  7. Nicolle says:

    Now do footballs.

  8. Kathy says:

    I am just not seeing the basketball as 4 cubic ft. I see it much closer to 1 cubic foot. Am I missing something?

    • jaylund says:

      People have more trouble comparing volumes than lengths, and more trouble comparing volumes of different shapes.

  9. Mick Klasson says:

    Thanks for this – I am aggrieved by water articles referring to a cubic foot as about the size of a single basketball, although I do like good visuals. Who could forget Jeff Mount’s description of the Eel River in flood releasing a mass of water “roughly equivalent to a herd of 15,000 Ford Country Squire station wagons thundering down the river canyon every second” in the terrific book California Rivers and Streams?

  10. Doug says:

    A single basketball is a quarter of a cubic foot (434 cubic inches), not four cubic feet.

  11. Another Brian says:

    The other common California water unit is the “unit” of course, often unhelpfully labelled as exactly that on your water bill, but it’s 100 cubic feet, also sometimes labelled CCF.

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