I want to treat the wetland in front of the house for mosquitoes but how much you use is based on how many gallons of water. How do I figure out how much water there is? The wetland is approximately 20’ x 40’ and the water is about 1’ deep.
Looks like it’s 7.48 gallons per cubic foot, such that 10x10x1 would be 748 gallons, which means that 40x20x1 would be 5984 gallons.
Can I ask what you use to treat it? I know next to nothing about this but I would be wary of using something that would work it’s way thru the food chain.
Would have thought that the surface area a better measure of treatment than the volume.
Thought that reference would have been to elfkin477rather than TOWP. Sorry.
And that as a proxy for included edge distance. I assume that the ‘wetland’ is vegetated, because a body of open water is a not a mosquito problem.
OP: I too wonder what kind of treatment you had in mind. Given that, as we speak, someone on this board is soliciting a math assignment ghost writer, my first reaction was to look to see you were a new contributor 
I’ve noticed a reduction in mosquitoes over the years since I put up bat houses.
This is one of those cases where the maths is quite straightforward in the metric system and much more complicated in non-metric. 20 by 40 feet is about 7 by 14 metres (rounded to the same precision as the original numbers), so covering that with water one foot (0.3 metres) deep gives you 7 x 14 x 0.3 = 30 cubic metres of water. Which is, of course, 30 tons, or 30,000 litres, of water.
I don’t know what you’re trying to use to treat mosquitoes by the gallon. Generally, treating the surface is the way to go.
Mosquito Dunks and Mosquito Bits are the easy, effective, and safe way to go. Widely available at Home Depot, Lowes, and in many garden supply stores. This is stuff that actually works – forget the other stuff you see.
Is there any case where the opposite is true? AIUI, the metric system was conceived to be easy to calculate with, while the imperial system (take what you like: temperature, coins, length, surface areas, volumes…) was conceived to… well… look over there! A squirrel!
Since 60 mph is a typical speed for long-distance drives, you can easily get the remaining time you need to drive - it’s as many minutes to your destination as you are miles away from it. But that’s a coincidence, not an intentional feature of the imperial system.
A case of a straightfowardness by design in imperial is the fact that the nautical mile is exactly one minute of arc along the meridian of the Earth, i.e., one minute of difference in latitude. The nautical mile was intentionally defined that way. This is useful for navigators when they calculate distances based on the astronomical observations they use to determine their position. Then again, the nautical mile is not strictly part of the imperial system, at least not how that term is usually understood.
I’ll accept the nautical mile, though few boats follow a route due south for long.
It’s one of Mosquito Dunk’s competitors, Amdro Mosquito Bombs. For reasons unknown they suggest one disk per 1500 gallons instead of surface area.
Most of the units in the “customary system” (or rather “customary systems”; the Imperial System and the American System are two of many examples) were designed to make one specific problem as convenient as possible. The problem is that they were all designed for different problems, and so there’s a really weird relationship between (for instance) a unit designed for measuring plow furrows in a field and the length from a typical man’s shoulder to his opposite fingertips (a furlong is 220 yards).
What’s the difference? In natural, human based measurements it is still length x width x depth in feet = cubic feet. Don’t know why the company decided to use gallons.
I’ve got one in my online cart for Home Depot 
Of course, this difference between 30,000 L and 5,984 gallons is 32% which is the biggest problem I have for the metric system you end up using decimals the whole time because their base units aren’t great for most things we measure. Though I prefer hL over bbls for brewery sizing.
The Amdro stuff is per gallon because it sinks in the water – the Dunks float on top (you can see when it’s gone).
You might have a hard time finding the ingredients in the Amdro – it contains (s)-Methoprene and carries a warning label regarding allergic reactions. Dunks have no warning label and no chemical poisons, only the bacterium which targets only mosquitoes, not other insects.
Note that Dunks and Bits won’t kill the mosquitoes you may already have; they only prevent the larvae from hatching, so if you have some of the Amdro spray (or any kind of mosquito fogger) that can quickly down any active mosquitoes in your yard.
No reason not to use up the stuff you’ve already bought but I suggest the Dunks or Bits for next time.
And a bat house is great idea. 
I’m not quite sure I get what you mean by “their base units aren’t great for most things we measure”. The difference between the 30,000 litres and the 5,984 gallons is solely due to rounding when I converted feet and inches into centimetres: I took the foot as 30 centimetres exactly, and then rounded the result to whole metres for the length and width of the area. But since the original measurements in feet were only approximate, the figure 5,984 gives a false sense of precision. You can’t have a result that’s more precise than the numbers you started with. The difference has nothing to do with any inherent features of the metric system.
Tosh and nonsense.
1mile+1 furlong+1 chain+1 rod+1 fathom+1 inch = 1837.5122 metres
1 hogshead+1 firkin+1 gallon+1 pint+1 schooner+1 fluid ounce=285.0076 litres
Calculations which are infeasible in the archaic units even if you know they are imperial/US or liquid/dry or Troy/Avoirdupois et al.
English units are also great if you want to divide by 3. If you have a 2ft long sub and three people to eat it how long is each person going to get. Answer 8 inches. If you have a 2 meter sub and three people to eat it each person gets 66.6666666667 cm (give or take an atom).