I am going to use this in planters that are approximately 14" x 14" to set 4x4x8s for patio lights. How many bags will I need?

Each 50 lb bag of QUIKRETE® Quick-Setting Cement will yield 0.45 cubic feet of material. QUIKRETE® Quick-Setting Cement is specially formulated to set in approximately 10–15 minutes. Do not mix more product than can be properly placed and consolidated in 5 minutes. For a slightly increased working time, QUIKRETE® Fast Setting Concrete Mix has the same yield of 0.45 cubic feet per 50 pound bag and has a typical set time of 20-40 minutes but will contain some gravel aggregate. Without the depth I cannot calculate the exact number of bags you will need for this application. For example, a 14 inch (1.167 foot) by 14 inch (1.167 foot) by 12 inch (1 foot) planter would require 1.36 cubic feet of material or 3 bags (of 50 lb each) of QUIKRETE® Quick-Setting Cement or QUIKRETE® Fast Setting Concrete Mix.