厚さ is read as あつさ (atsusa) and means thickness.
あつさ
atsusa
こうせい
(former) Ministry of Health and Welfare
あつい
abundant
あつがみ
cardboard
こうせいねんきん
welfare pension
こうせいしょう
こうしょう
Welfare Minister
こうい
kindness
あつぎ
wearing thick clothes
あつみ
thickness
あつかましい
impudent
あつで
thick (paper, cloth, etc.)
あついた
plank