noun
inside measure; internal dimension
Refers to the clear internal measurement of a space, such as the width or depth inside a container, room, or frame, as opposed to the external dimensions.
この箱の内法は縦30センチ、横20センチです。
The inside dimensions of this box are 30 cm by 20 cm.
建築図面には内法寸法が記入されている。
The architectural drawings show the internal measurements.
外法 refers to the external or overall dimensions, while 内法 is the clear internal measurement.
Compound of 内 (uchi, 'inside') and 法 (nori, 'rule, measure'). The reading のり for 法 is an older native Japanese reading used in measurement contexts.