for 100 ft fence length how many times need to refill the Cup

Would you recommend this sprayer for 350 feet lin feet.

It will really depend on the height of the fence, as the answer really depends on the total surface area to be covered. Under most circumstances, you will likely see 200-250sq. ft. per gallon while spraying, with variances for how thick you lay the material on. A 1 qt. container would cover approximately 1/4 of that, or around 50-60 sq. ft on average.

Depending on how fast you move and how well you work the unit, you should be able to get about 10-12 feet of planks and boards on 1 side per fill. So roughly 10 refills per side. There are other factors like the type of wood your covering and the extent it needs to be sprayed. This is a rough estimate. My coverage estimate was based on a 4' 3/4" dog ear style privacy board and 2x4 planks with 4x4 posts. I did 350 feet and used about 4.5 gallons per side. It was my first time using the sprayer. Might shave that down some next time.