A lot of older posts pointing the answer: steem_per_mvests to steemd.com, but it seems they stop calculating this "steem per million vests" anymore. Instead, they publish SPV (steem per vests).

Vesting fund
191,500,815 STEEM
389,306,005,511 VESTS
0.000491903 SPV

You can also download the vesting fund data and calculate it yourself from https://steemdb.com/api/props, I found this on this post.

update: you can also pull all kinds of conversion rate from steempy:

3.3.5 Converter
class steem.converter.Converter(steemd_instance=None)
Converter simplifies the handling of different metrics of the blockchain
rshares_2_weight(rshares)
sbd_median_price()
sbd_to_rshares(sbd_payout)
sbd_to_steem(amount_sbd)
sp_to_rshares(sp, voting_power=10000, vote_pct=10000)
sp_to_vests(sp)
steem_per_mvests()
steem_to_sbd(amount_steem)
vests_to_sp(vests)

I hope this will save you some times if you're looking for the same thing.