TurfGrassPro 25 - 0 - 0 is not mixed per gallon but is per area as water is just the carrier.   For Cool and Warm Season Turf: Apply 2-8 oz. per 1000 ft. sq. in 3-5 gallons of water.   You would calibrate by determining the volume of water required to treat 1,000 square feet. Use this calibration volume to determine the amount of water and fertilizer needed to treat the target area (see the following calibration example). Note: Sprayer calibration (volume of spray needed to treat 1,000 square feet) will vary with each individual operator. Steps in Calibration:
1. Mark an area of 1,000 square feet (i.e. 20 by 50 feet or 25 by 40 feet).
2. Place the sprayer on a level surface and add water noting the final level of water in the spray tank.
3. Spray the marked area with a sufficient volume of water to provide uniform coverage. Refill the sprayer to the same level as before measuring the amount of water added. The measured water added to the sprayer is the volume needed to cover 1,000 square feet.
4. Determine the application rate (fl. oz./1,000 sq. ft.)  from the nutrients needed
5. To each volume of water used as measured in step 3, add the amount of product as determined in step 4.