KitchenAid 30" Installation Instructions And Use & Care Manual page 6

Countertop Cutout Dimensions
IMPORTANT: Countertops with a bull-nosed front edge are not recommended for these installations.
Some models require a countertop deeper than 25" (63.5 cm); see the following Countertop Cutout Dimensions Chart.
To avoid mistakes, it is recommended that the cooktop and vent cutouts be drawn on the countertop before making any cutouts.
See Cooktop Installation Instructions for complete cutout dimensions, location dimensions and installation details.
A. Downdraft vent
B. Cooktop
C. Measurement of cooktop rear overhang.
D. D = Measurement of cooktop rear overhang (C) + 1
(E)
Countertop Cutout Dimensions Chart
A. ½" (12.7 mm) minimum to backsplash or
B.
6
B
B
A
rear wall
³⁄₄
" (19.1 mm) maximum backsplash depth
D
E
F
C
G
A
I
E. 1
F. ½" (12.7 mm) minimum
G. ¼" (6.4 mm) minimum
¹³⁄₁₆
" [46.2 mm] H. Countertop and backsplash
I. ½" (12.7 mm) minimum
D
C
¹⁄₂
C. 27 " (69.9 cm) on 30" (76.2 cm) models
¹⁄₂
33 " (85.9 cm) on 36" (91.4 cm) models
D. D = Measurement of cooktop rear overhang
¹³⁄₁₆
+ 1 " (46.2 mm)
H
¹³⁄₁₆
" (46.2 mm)