Generally speaking what size in gallons sprayer with boom or boomless does one need to cover a 2 acre field with glyphosate to kill weeds?
OR
How many acres would a 50 gallon sprayer cover?

It all depends on the pressure, nozzle size, your speed and then the mix in the tank. I used a 15 gallon sprayer with 1pt to 1qt of glyphosate to 15 gallons of water to cover just over an acre to 1.5 acres. I had a boomless nozzle to spray weeds/grass in foodplots. The mix rate depended on how thick and how tall the vegetation was I needed to kill.

Others will most likely know more than I, but it takes me 55 gallons to cover 2 acres with my set up.

I've never had a sprayer that was worth the money. So finally this is what I did.

I am totally inept when it comes to tools and making stuff, so If I can put this together, so can you. It is very simple to make. I went through two sprayers that I bought, one at tractor supply and one at Atwoods in 3 years. They just don't hold up. I paid $299 for each one. Hose's rotted, tank got a hole in it from bouncing over the ground full of water, tires went flat from weight of water. Just did not hold up.
So, here is what I came up with and it cost me about $125 and I have used it for the last 3 years. Now that cost is not completely accurate
as I already had one of the main parts.
A battery jump starter to run the 12v pump. Of course any 12v battery would work also.

Now here is what I had to buy.
1. 55 gallon plastic barrel...$15
2. two 6' hoses...$12
3. two 4' sections of pvc, two joint sections of pvc, two water sprinkler heads,(not the whole head, just the dial part), and a T section of pvc that had a hose connection. $15
4. A water pump..$80..

I ran one hose to the barrel from the pump, and one hose from the pump to my pvc sprayer. I hope the photos can give you a better ideal of what I am talking about.

Technically a sprayer should be calibrated before you use it - speed, swath, pressure, nozzle size - all play into it. It's not hard to calibrate one but you need two people (one person to drive whatever you're spraying with, one person to hold a measuring jug over a nozzle - obviously use water to calibrate), a measuring jug, and a 100' tape laid out. It's just a basic math formula...it's a PITA, but generally a one time deal unless you're spraying legit stuff that really matters or is very specific on the application rate. I know with my 300 gallon sprayer if I drive at x speed at x pressure I'm going to put out 25 gallons per acre.

If you are spraying for broadleaf weeds with something like 2-4D, pasture pro, etc., then I use a pint per acre with 12-15 gallons of water per acre.

If you time how long it takes to travel the distance you are using to calibrate, you can easily calibrate by yourself while sitting still.

Because the concentration of glyphosate can differ greatly from one product to the next, I always check the label for the recommended mix rate. The last time I checked, one of Tractor Supply's store brand offerings was the best deal in terms of price for the highest concentration per volume.

Don't forget to add a little dish soap so that it sticks better to whatever you hit with it. I suspect the more expensive stuff already has a surfactant added to it.

My Boomerator Noozle came with a instruction sheet that is pretty close. Match your nozzle to Ground speed, pressure pump is set on and how much material per acre. Sprayed them dang army worms again today.

Been horrible this year.
I've had them move in twice already and the first time I had to spray 2 days in a row there was so many. They were tiny but in my grass by the millions.

Usually we do not see them at our place until late September or even October. I believe the abundance of rain and cooler than normal temps had them out early. They can devastate a field of coastal in 12 hours.

Nozzles size also open up with usage, so It won't have the same output or droplet size forever.