If you are using organics, you really don't have to be exact anyway. Pick a low setting and spray away. The worst thing that will happen is that you will have to stand out there spraying for a bit. If it is taking you forever to cover the area, dial it up a bit.

Anyway, my rule of thumb would be to start low and adjust upward as necessary. Seaweed is usually on the expensive side, so I wouldn't want to accidentally overapply. It wouldn't hurt the grass, but your pocketbook probably wouldn't appreciate it.

If you are really into precision or calculations....

Determine the gallon/minute flow rate of your hose and sprayer. Basically, just turn the setting to "0" and spray into a couple gallon bucket and see how long it takes to fill it. You'll know the size of the bottle you are applying (probably listed in ounces) and they usually list approximate coverage rates. From that, you can pick an application rate (like 1 oz per gallon) and determine how to spray - eg, your hose puts out 2 gallons per minute. At a 1 oz per gallon setting on the sprayer, that would put out 2 oz per minute of product. If 8 oz is supposed to cover 1000 sq ft, then you would know you should be spraying for about 4 minutes for that size area. In that case, you would probably want to pick a slower flow rate - maybe 0.5 oz per gallon - so it don't have to race around the yard.

This was very helpful. Thank you very much for the reply.

I just fill in equal parts of molasses, seaweed and apple cider vinegar set at 2oz setting and just spray away till the container is empty. Repeat it on another lawn. Ortho dial sucks up more quickly than you realize so that's why I have a full container of all these things so I won't overapply seaweed alone.

The compost tea rate suggested in most of the stuff I read is 5 gallons per acre. That converts to roughly a pint per 1,000 square feet. If you put a quart of tea in your sprayer, measure out 2,000 square feet and spray that area until the sprayer is empty. The setting on the dial makes no difference at all if you apply the proper measured amount to the proper measured area.

The only seaweed application rate I've ever heard is 3 ounces per gallon sprayed with a hand sprayer to moisten foliage. You can set your sprayer for 3 ounces per gallon and spray, but that rate doesn't tell you how much to apply per 1,000 square feet. If all you were doing was moistening the foliage and not saturating the soil, you could be finished pretty fast and not use much seaweed. Part of the beauty of using a Ortho type sprayer is you can fill it up with undiluted product, spray what you need, and pour what you don't use back into the original bottle without worry of contamination or dilution.

now I am confused :-)

I think I will just come back and ask again the next time I am going to spray something, lol.

Well, are there people who can assist you in the application settings where you buy the solution? IF it's not on the label, can you google the web and get some kind of input other than here? I have the same applicator and I usually use the 2oz setting for most applications, but again that may be too much for an expensive solution. Just a little more confusion for you. :)