**Friends, you may have noticed** that we have recently entered a period of what is euphemistically called “enhanced risk of wildfires”.

**And reports of wildfires** from around the world include some truly apocalyptic images.

**But many of these reports fail** to communicate clearly one of the key metrics for fires: the size of the fire.

**Some reports do mention the area** affected in hectares (abbreviated as ha) or acres, but while I can just about grasp the meaning of one acre or one hectare – I struggle to appreciate the size of a fire covering, say, 6,000 hectares.

**In order to convert these ****statistics** to something meaningful, I work out the length of one side of a square with the same area.

**Areas expressed in hectares.**

**A hectare is an area** of 100 m x 100 m, or 0.1 km x 0.1 km so that there are 100 hectares in a square kilometre.

**So to convert an area** expressed in hectares to the side of the square of equal area one takes two steps.

- First one takes the square root of the number of hectares.
- One then divides by 10.

**So for a fire with an** area of 6,000 hectares the calculation looks like this:

- √6,000 = 77.4
- 77.4÷10 = 7.74 km

**Since the original area** was probably quite uncertain I would express this as being equivalent to a square with a side of 7 or 8 km.

**Areas expressed in acres.**

**An acre is an area** of 63.6 m x 6.36 m, or 0.64 km x 0.64 km so that there are roughly 2.5 acres in a hectare.

**I can’t think** of an easy way to get a good approximation for acres, but a bad approximation is better than no estimate at all. So I recommend, the following 3- or 4-step process:

- First one divides the number of acres by 2
- Then one takes the square root of half the number of acres.
- One then divides by 10.
- This answer will be about 10% too large.

**So for a fire with an** area of 15,000 acres the calculation looks like this:

- 15,000÷2 = 7,500
- √7,500 = 86.6
- 86.6÷10 = 8.7 km

**At this point one can **either just bear in mind that this is a slight over-estimate, or correct by 10%. In this context, the overall uncertainty in the estimate means the last step is barely worthwhile.

**How bad is the situation in Europe?**

**There is a wonderful website (link) **which publishes estimates of wildfire prevalence in all the countries of the EU. One output of the website is shown above:

- The
**blue bars**shows the average area burned from 2006 to 2021 - The
**red bars**shows the average area burned so far this year.

**You can immediately** see that Spain, Romania, and France are having bad years for wildfires.

**But how big an area** is 244,924 hectares – the area burned in Spain so far? Using the rule above, one can see that it is an area equivalent to a square with a side of 50 km – roughly equivalent to (say) the area of Cheshire.

**The area burned in France** so far this year is 60,901 hectares. Using the rule above, one can see that it is an area equivalent to a square with a side of 25 km.

**Michael, what was the point of this article?**

**When trying to visualise large areas **expressed in hectares (or acres) I find it useful to work out the length of side of a square which would have the same area.