$/Mhash - that's a new one. Well, the metric used elsewhere is Mhash/$ which answers the question how much hashing a dollar's worth of a piece of equipment will produce. So if you really wanted $/Mhash (for referencing cost of certain equipment) then you could invert any Mhash/$ and get $/Mhash.
Or, perhaps you are asking how many dollars are earned for doing the work of a million hashes?
If so, here's how:
1.) Determine the difficulty:
2.) Compute total hashes per second:
1,726,566 * 2^32 / 600 seconds = 12.4 Terahashes occurring per second.
There are 1,000 Ghash per Terahash, and there are 1,000 Mhash per Ghash.
so there are 12,400,000 Mhashes occurring per second.
(i.e., if all mining were done with AT HD 5830s, there would be about 45,000 of them hashing away.)
3.) Determine the value of bitcoins issued per second (using current exchange rate):
- BTC/USD * 50 BTC / 600 seconds = BTC/USD per second.
Currently: $6.45 X 50 BTC per block / 600 seconds = value of $0.5375 USDs per second.
4.) Determine value per Mhash
$0.5375 / 12,400,000 = $0.000000043 $/Mhash
That's a pretty small number. But that's the revenue $/Mhash at the current difficulty and exchange rate.
So your 5830 does in the range of 275 Mhash/s, so it generates (gross revenue):
- 275 Mhash/s * $0.000000043 $/Mhash = $0.000011825 USD per second.
Per day then:
Compute number of seconds per day:
- 60 seconds/minute * 60 minutes/hour * 24 hours/day = 86,400 seconds per day.
86,400 * $0.000011825 = $1.02168 USD per day (or about 0.1584 BTC).
So each 5830 will see gross revenue (at current difficulty, exchange rate and block reward) of:
$1.02168 USD/Day * 365 Days/Year = $372 / Year.
Well ... not quite. We know that around the beginning of December the block reward drops in half. So that $372 in gross revenue now becomes about $273.
Of course, you need to subtract your cost of electricity. And since you don't know the future difficulty level or future exchange rate either, it cannot be known how long it will be before you break even.
But let's say you have a beefy power supply, mobo that can accommodate 5 PCI-e, and each 5830 drawing 175 Watts, plus fans say you consume a thousand watts.
- 1,000 watts * 24 hours/day / 1000 Watts/kW = 24 kWh/day
So per-day, if you pay $0.15 (national average, residential power), your electricity costs:
- 24 kWh/day * $0.15/kWh = $3.60 per day (for a rig with five 5830s)
The gross revenue for each 5830 is $1.02 per day X 5 = $5.10, leaving gross profit of $1.50 per day for all five together.
But then beginning in December, you cannot mine profitably. Your cost of electricity remains the same, but the per-block drop means your gross revenue drops by half, to $.51 per day per 5830, or $2.55 for all five 5830s.
So you would be paying $3.60 in electricity to earn $2.55 in bitcoins.
The only GPU mining operators left standing will be those whose electricity rate is significantly below average or those whose electricity is included in the rent that would be paid regardless.