Every 14 days, on average, the Bitcoin difficulty is adjusted, to make the time between blocks stay near 10 minutes.
Real-time data about bitcoin difficulty is posted here:
https://bitcoinwisdom.com/bitcoin/difficulty
The chart below shows recent difficulty adjustments (the red line):
From the same source, the current Bitcoin difficulty is
199,312,067,531
What does that number mean? The
official explanation
is very confusing.
A forum post offers this simple formula to convert this difficulty value to bits:
log2(difficulty) + 32
So the current difficulty is:
log2(199,312,067,531) + 32 = 69.53 bits
The latest hash calculated is for
Block #414793
with this value:
00000000000000000530216a17ab1e11502720c784975dc7618f8408df6f7c77
Adding spaces every 4 digits makes it easier to count the zeroes:
0000 0000 0000 0000 0530 216a 17ab 1e11 5027 20c7 8497 5dc7 618f 8408 df6f 7c77
There are 17 zeroes, each representing 4 bits, for a total of
68 bits. The next hex-digit is 5,
which is less than 8, so there's one additional zero
bit for a total of 69 zero bits.
Clearly, that formula works.
2^69.53 / 10 min = 1,420,000,000 Giga-hashes per second
This is quite close to the
actual current hash rate
of 1,426,731,353 GH/s.