So 1" of sand for a 250 sq ft patio, would take 83 bags???

Yes. The description clearly states that 1 bag will cover approximately 3 square feet at a depth of 1 inch.

it says one bag is 0.5 cubic feet. that means it will fill 1'x1'x6" box. that means if your box is 1'x1', but only 1" deep, you can feel 6 boxes like that. that means with one bag, you can fill 6 sq feet, 1 inch deep. 250sq f /6= 41.7 bags. you will need 42 bags.

The item description states that one bag will cover 3 square feet 1" deep. I just confirmed that with Lowes and they said it would take 83 bags for my 250 sq ft project. 250 sq ft divided by 3 sq ft = 83.33 bags.

You need to convert to cubic feet unit. So 1 inch depth will be 1"/12"=0.083 ft. 250 sq ft x 0.083 ft=20.83 cu ft 20.83 cu ft / 0.5 cu ft/bag=42 bags