Japanese Map Kyoto 1696
Determining the floor area for the purposes of regulations or construction in Japan, can be complex. Here you will find a brief introduction to the most common definitions you will need to be aware of, when planning  in Japan.


Floor area calculation system in Japan


A 敷地面積 Shikichi menseki - site area; lot area; lot size




B 容積対象床面積 Youseki taishou menseki (容積対象面積)


Defined by the center line of the outer wall or column, included technical spaces on the roof ペントハウス(PH) and ducts パイプスペース(PS). Excluded: elevator (エレベーター室), open spaces, external staircase. It is used for calculating the floor area ratio 容積率.




B1 容積率 yousekiritsu floor area ratio (FAR)






C 建築面積 Kenchiku mensekibuilding coverage area


Defined by the center line of the outer wall or column, open areas are not included.Therefore, balconies, verandas, and eaves are not included in the building area, till the depth of 1 meter (for example, if the total width is 1 meter and 40 centimeters, 40 centimeters are included). The "bow windows" at a height of 30 cm or more from the floor, and less than 50 cm out from the wall are not counted. Balconies and verandas surrounded by walls on three sides are included.


The building coverage area 建築面積 is defined by the Building Standards Law, and it is used for calculating the building coverage ratio 建蔽率.




C2 建蔽率 or 建ぺい率 Kenperitsu (BCR)% = building coverage area / site area × 100






D 容積対象外床面積 = 駐車場 + エレベーターホール + 屋内廊下 + 屋内階段


Yōseki taishō-gai tokomenseki = chūshajō + erebētāhōru + okunai rōka + okunai kaidan


Excluded Floor Area = Parking + Elevator + Indoor Hallway + Indoor Staircase




E 延べ床面積 nobeyukamenseki - total floor area (延床面積)


延べ床面積= 容積対象床面積 + 容積対象外床面積


Nobe tokomenseki = yōseki taishō tmenseki + yōseki taishō-gai tokomenseki


Total Floor Area = Volume Floor Area + Excluded Floor Area




F 施工床面積 = 延床面積 + 外廊下 + 外階段 + バルコニー


shikō yuka menseki Nobe tokomenseki + soto rōka + tokaidan + barukonī


Construction floor area Total floor area + outside corridor + outside staircase + balcony




Building Coverage Ratio (BCR) 建蔽率 Kenperitsu and the floor area ratio (FAR) 容積率 yousekiritsu

Each zone restricts the building size and density by prescribing the numbers used to calculate the buildable area  建蔽率 Kenperitsu and  容積率 yousekiritsu (Building Coverage Ratio - BCR and floor area ratio - FAR).

The purpose of the BCR 建蔽率 or 建ぺい率 Kenperitsu is to limit building density, preventing fires from spreading between adjacent buildings; ensuring light and air penetration; controlling urban character.

Kenperitsu (BCR)% = building coverage area / site area × 100

Japan has extensively adopted the floor area ratio in the zoning system since 1970. Some say that it has deteriorated the skylines and building lines in Japanese cities, others claim that it has protected the residential environments. The floor area ratio (FAR) – yousekiritsu 容積率 – sets the maximum possible floor area, totalled across all floors and expressed as a percentage of the site area. In other countries Floor Area ratio is sometimes called floor space ratio (FSR), floor space index (FSI), site ratio or plot ratio. The difference between FAR and FSI is that the first FAR a ratio, while the FSI is an index. For example 250% FAR is 2.5 FSI.

Yousekiritsu (FAR)% = total floor area / site area × 100

When constructing buildings across multiple zones with different prescribed ratios, in Japan, BRC and FAR  should be calculated with a weighted average.


Where to get informations

This guide is by no means complete, is just a quick overview of aspects of Japanese Building Standard Law. It is also a way l to show how things can be done differently.


yousekiritsu floor area ratio (FAR)


Kenperitsu = building coverage area (BCR)








都市計画区域内(■市街化区域 □市街化調整区域 □区域区分非設定)

準都市計画区域内 □都市計画区域及び準都市計画区域外

4.防火地域】 ■防火地域 □準防火地域 □指定なし



【イ.幅員】西側:米谷昆陽尼崎線 18.0m

【ロ.敷地と接している部分の長さ】 18.25m


.敷地面積】 (1)( 250.88 )( )( )( )

(2)( )( )( )( )

【ロ.用途地域等】 ( 準住居 地域 )( )( )( )


( 200.00 )( )( )( )


( 60.00 )( )( )( )

【ホ.敷地面積の合計】 (1) 250.88





8.主要用途】 (区分 08030 ) 店舗付き共同住宅(駐車場付き)


新築 □増築 □改築 □移転 □用途変更 □大規模の修繕 □大規模の模様替

10.建築面積】 (申請部分 )(申請以外の部分 )(合計 )

【イ.建築面積】 ( )( )( )


11.延べ面積】 (申請部分 )(申請以外の部分 )(合計 )

【イ.建築物全体】 ( )( )( )

【ロ.地階の住宅の部分】 ( )( )( )


( )( )( )

【ニ.自動車車庫等の部分】( )( )( )

【ホ.備蓄倉庫の部分】 ( )( )( )

【ヘ.蓄電池の設置部分】 ( )( )( )


( )( )( )

【チ.貯水槽の設置部分】 ( )( )( )

【リ.住宅の部分】 ( )( )( )

【ヌ.延べ面積】 ㎡