A cubic planter with sides of 14" = 14 * 14 * 14 = 2,744 cubic inches.
2,744 * .95 = 2,606.8 cubic inches for 95% full.
Planter 1 = 2,744 * .40 = 1,097.6 cubic inches in it. 2,606.8 - 1,097.6 = 1,509.2 still needed.
Planter 2 = 2,744 * .70 = 1,920.8 cubic inches in it. 2,606.8 - 1,920.8 = 686 still needed.
Planter 3 = 2,744 * .85 = 2,332.4 cubic inches in it. 2,606.8 - 2,332.4 = 274.4 still needed.
Planter 4 = 2,744 * .90 = 2,469.6 cubic inches in it. 2,606.8 - 2,469.6 = 137.2 still needed.
1509.2 + 686 + 274.4 + 137.2 = 2,606.8 more cubic inches of soil needed.
