Fruit tree spacing depends entirely on the grower's needs and objectives. Four- to ten-foot spacings are all common in backyard plantings. But if your goal is simply to have a steady supply of fresh fruit for family use, fruit trees planted 3-4 feet apart in groups or rows (and given summer pruning for size control) will provide plenty of fruit during their harvest period. A group of four trees in a 10'x10' space can give fruit for two months or more.
Fruit trees may be planted as close as 18 inches apart in order to have more kinds of fruit ripening at different times in a small space in the yard. Trees espaliered against a fence or wall require very little space.
For more information about spacing home fruit trees, see Backyard Orchard Culture.