Why are wildfire sizes reported in acres?

There are a total of 49 terrible wildfires currently blazing away in Alberta, Canada. While fortunately there have been no deaths and injuries, the damage has been extensive. This news report begins by describing the extent of the fire.

A huge wildfire raging in the Canadian province of Alberta has grown to 85,000 hectares (210,035 acres) in size and officials would like to move south about 25,000 evacuees who had previously fled to the north.

I was curious as to why news reports of fires tend to use acres and hectares as measures of the extent. I personally have little sense of how big an acre is and absolutely no idea what a hectare is. There was time in school where I knew off the top of my head the conversion factors for most areas but that was long ago. Now I have to look it up to get a better sense of how big it is. I first convert the acreage to square miles, then take the square root of that number, and this enables me to envisage a square of that size because it gives me a comparison with the distances in my town. In this case the fire covers 328 square miles or a square of side 18 miles

Maybe for people who live in rural and farm areas where these fires usually take place or those who own houses that occupy a lot of land, the acre is a unit that they can easily envisage. But hectares? Is that a common measure of area for anyone at all?


  1. fraocheilean says

    Hectare is a standard metric measure. 1 hectare = 10,000m^2, i.e. 100 m on a side.

  2. says

    What else would be a useful metric of how big the fire is?
    Tree count? $$ damages? Deaths? CO2 footprint?

    I’m fascinated by metrics and how humans generally converge on something that does a pretty OK job of conveying whatever it was intended to convey. Sometimes we get it horribly wrong. Acres/hectares/square miles seems pretty good to me.

  3. moarscienceplz says

    This may or may not be helpful to you, Mano, but I just remember that an acre is about the size of an American football field, not counting the endzones.

  4. Dean says

    I suspect that it is a convenient measure of a large area without needing to go to unusually small numbers or large ones.

    For instance, if they were measured in square kilometres, most large areas would actually require small fractions…a football field would actually be about 0.01 square kilometres. If you were measuring in square metres though it’d be 10,000 square metres.

    And according to http://cwfis.cfs.nrcan.gc.ca/ha/nfdb the vast majority of forest fires are less than 200 hectares.

    And since acres are about half the size of a hectare, this reasoning follows for those as well.

  5. anat says

    Dean, that’s why in Israel a common unit of area is the ‘dunam’ -- 1000 square meters (roughly a quarter of an acre).

  6. coragyps says

    Mano, it’s real simple! An acre is the area of a square piece of land that’s 208 feet, 8 and 67/128 inches on a side, approximately! Or of a rectangle 110 by 396 feet, exactly! Easy-peasy!

  7. says

    Fortunately, hectares to square kilometres is easy (divide by 1000). Square km is definitely easier for the majority of people to visualize. So why does the media not use Sq. km when speaking to the general public? To make it sound larger than it is?

    Probably. The media live by the bloodthirsty maxim, “If it bleeds, it leads” for news stories. I bet “If it burns, it earns” applies to fire and disasters.

  8. Raucous Indignation says

    Google had some fascinating tidbits. Yes, one hectare is 1⁄100 km2. But now I also know that the maximum playing area of an international-sized rugby union pitch is about one hectare.

  9. DonDueed says

    The fire in Alberta has been expressed in multiples of Manhattan. The latest comparison I’ve heard is “bigger than New York City”.

    Somehow that makes it seem smaller to me. NYC is very big, but not gigantic.

  10. Holms says

    I suspect it is similar to the way here in Australia, which went metric decades ago, people’s heights are still very often given in feet / inches, even if the it has to be written in metric for the purposes of statistics. It’s partly because it is a convenient-ish unit for the thing being measured, but I suspect mostly because that’s just how it has been throughout people’s lives. The oldies who can remember metrication use the habit they grew up in, which in turn means the young ‘uns steeped in the same habit despite it no longer being official. Such changes are likely to be very gradual.

  11. WhiteHatLurker says

    Land in Western Canada was surveyed on a mile grid(*), each square mile is 640 acres (or 160 for a quarter section). It’s a familiar measure to those who live here.

    As a correction, there were two deaths in the evacuation.

    (* With exceptions. Original land surveys were in river lots, but that is probably more detail than is required.)

  12. machintelligence says

    Same here in the USA.
    There are 640 acres to the square mile. This is also the “section” on survey maps. When i was in Germany I asked about how many hectares there were on a farm and found that they use a much older measure the “taggenwerk” (day’s work — but my spelling may be wrong.) Farmers are quite conservative people, I guess.

  13. lorn says

    Reminds me of the old joke where a guy is talking about how big his ranch is and tells his friend it is so big ‘it takes him all day to drive across in his pickup truck’. His friend answers back that the used to have a truck like that.

    An average person walking for an hour covers a league. A league is roughly three miles. I take an hour long walk pretty much every day so I have a good feel for a league.

    I used to teach apprentices that they needed to have a feel for measurements. A hand-span is roughly 8″ or 20cm. A fist with thumb extended is roughly 6″, 15cm. An arm-span is roughly 6′, 1.8m.

  14. hyphenman says

    In general, for those of us stuck with the English system of measurement, we’re simply not used to thinking about areas bigger than square yards (common when buying carpeting). I grew up in farm country so I think in acres, but ruralites are becoming fewer and fewer ever year.

    Jeff Hess
    Have Coffee Will Write

  15. Lofty says

    A hectare is a logical unit of land in countries that have mastered the metric system requiring only a decimal point shift to convert to other useful units, like square metres and square kilometres.

  16. Mobius says

    Inside the US, I don’t see a hectare having much meaning, but outside the US the metric system is the rule and hectare does have meaning.

    But it would seem to me that acre/hectare gives a larger, more alarming number.

  17. grendelsfather says

    You think acres are bad? Just last month I sold an easement for a natural gas pipeline on some land I own in Texas, and I was paid by the rod. According to Wikipedia, “The rod or perch or pole is a surveyors tool and unit of length equal to 5 1⁄2 yards, 16 1⁄2 feet, 1⁄320 of a statute mile or one-fourth of a surveyor’s chain and 5.0292 meters. The rod is useful as a unit of length because whole number multiples of it can equal one acre of square measure.” Yes, what a useful unit!

    I remember learning about rods and chains in school, but I had no idea that anyone still used them.

  18. Trebuchet says

    @6, Coragyps:
    Mano, it’s real simple! An acre is the area of a square piece of land that’s 208 feet, 8 and 67/128 inches on a side, approximately!
    It makes more sense if you multiply that number by the square root of 10. And I’m not joking about that.

  19. ivo says

    When i learned the metric system in primary school, they told me an hectar is a practical unit for land areas because you can visualise it as a football (=soccer) field.

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