Standard side-mount slides need 1.0" total (0.5" per side).
Usually 0.5" or 0.75" plywood/hardwood.
Cut List
Sides (Quantity: 2) Length x Height
20" x 4"
Front & Back (Quantity: 2) Length x Height
10" x 4"
Bottom Panel (Quantity: 1) Width x Depth
10.5" x 20.5"
Construction Note: These calculations assume the "Sides run past Front/Back" method. The Front and Back pieces are sandwiched between the Sides. The bottom calculation assumes the groove is cut on all 4 pieces.