Well-known Synonym: 打墙也是动土 打墙也是动土
http://zhidao.baidu.com/question/70931373.html?fr=ala&amp;word=打墙也是动土&amp;device=mobile&amp;ssid=0&amp;from=844b&amp;uid=0&amp;pu=usm@0,sz@1320_2001,ta@iphone_1_8.4_3_600&amp;bd_page_type=1&amp;baiduid=B0DC14BD4CFD809A8478494C15B38C6D&amp;tj=zhidao_1_0_10_l1

动土：指破土建房。意谓为了小事费了大手续，便不如索性做起大事来。
出处：《红楼梦》第二十九回：“‘打墙也是动土’！已经惊动了人，今日乐得还去逛逛。”

ABC

Lit Building a wall also [requires] moving earth.
Fig Building a wall requires almost as much work as building a house, so why not build a house? If one is going to undertake something, why stop at half measures? Why not “go the whole hog”/go “all the way”?

打墙也是动土 doesn't seem to be super well known, I'm looking for something that expresses the idea of &quot;If one is going to undertake something, why stop at half measures?&quot;.
Any synonyms?
Besides 一不做，二不休, there is 好人做到底，送佛送到西. Or simply 既然已经做了，索性做到底. 

In English you can say "in for a penny, in for a pound".