Justice Breyer is often described as a left-of-center moderate. One way to measure this is to see how often he votes with the other left-of-center Justices, rather than the right-of-center Justices. SCOTUSBlog’s statpacks helpfully measure the Justices’ agreement in 5-4 cases (this considers agreement in full, part, or judgment only–the broadest measure SCOTUSblog records).

	Roberts	Scalia	Kennedy	Thomas	Ginsburg	Alito	Sotomayor	Kagan
OT 14	26%	5%	47%	11%	89%	21%	95%	79%
OT 13	20%	0%	50%	20%	70%	30%	80%	80%
OT 12	26%	4%	43%	22%	78%	23%	73%	78%
OT 11	27%	7%	47%	20%	87%	20%	73%	79%
Average	25%	4%	47%	18%	81%	24%	80%	79%

In 5-4 cases, Justice Breyer agrees with Justice Ginsburg, Sotomayor, and Kagan around 80% of the time. He agrees with Justice Kennedy half the time. He agrees with CJ Roberts 25%, with Justice Scalia 4%, with Justice Thomas 18%, and with Justice Alito 24%.