How long do the resources last in a Starcraft 2 base?

In a standard SC2 league map, how long do the mineral patches and vespene geysers last? I know that you should start expanding before the resources start to dry up, and so I'm curious what the time frame is.

I'm curious how long they last at your starting base (assuming you continuously produce workers until you have 30 to saturate collection), and how long they last in an expansion site, where you start by sending about 10 workers there, and then build more until 30ish.

Using the numbers tzenes gave:

• Start out with 8 mineral patches, each with 1500 minerals
• Start with 6 SCVs (right?)
• An SCV takes 22 seconds to build
• The first 2 SCVs on a mineral patch will gather 45 minerals a minute each, while the last one can be considered to gather about 12

In other words, there are 12,000 total minerals to gather; the first 16 SCVs will gather 45/min, the last 8 will gather 12/min. Using this knowledge (and not taking MULEs into consideration!), we can construct a table:

 Seconds  | Number   |  Resource gather rate  |   Total minerals
 elapsed  | of SCVS  |  (minerals / minute)   |  gathered (approx)
------------------------------------------------------------------
        0 |     6    |          270           |        0
       22 |     7    |          315           |       99
       44 |     8    |          360           |      214.5
       66 |     9    |          405           |      346.5
      ... |   ...    |          ...           |      ...
      198 |    15    |          675           |     1485
      220 |    16    |          720           |     1732.5
      242 |    17    |          732           |     1996.5
      ... |   ...    |          ...           |      ...
      374 |    23    |          804           |     3672.9
      396 |    24    |          816           |     3967.7

So at the time your 24th SCV is built and you become fully saturated, you could have mined about 3968 minerals. The remaining 8032 will then be mined in about 590 seconds, giving an overall time of 986 seconds, or about 16 and a half minutes.

Of course, this is a lower bound. In a real game, the actual time will be slightly longer because:

• Some SCVs will be building/scouting
• Some SCVs will be mining gas instead
• Not all mineral patches will deplete at the same time, so your resource gather rate will actually go down near the end. Hopefully by this point, you have several other expansions :)

So there are a number of variables involved here, but I'll try to help you out:

• Standard base has 8 mineral patches
• Each mineral patch has 1500 minerals
• If you have 2 SCVs on a patch they harvest ~90 minerals per in game minute (depending on distance)
• Standard base has 2 Vespene Geysers
• Each Geyser has 2500 gas
• 3 SCVs harvest at 101-114 gas per in game minute

Here is the problem: when you have more than 2 SCVs per patch they start to ping pong around between patches. At this time your SCVs harvesting rate starts to become indeterminate. However, we can calculate an upper bound on the time it takes if you have at least 16 SCVs mining minerals. 1500/90 = 16m 40s. We can further provide a better estimate based on the fact that, on average, 3 SCVs harvest at ~102, giving us 1500/102 = 14m 42s. Gas takes understandably longer to mine out because of its higher amount, on average: 2500 / 107.5 = 23m 15s.

Both of these numbers are further influenced by: Distance of minerals to based, number of workers transfered, distribution of workers transfered, build rate of new workers, use of chrono boost and infuse larva, number of worker producers, resource gain rates, and MULES.

Its also worth noting that the influence of workers beyond the 16th is significantly reduced according to this table:

• One SCV on one mineral patch harvests 39-45 minerals per game minute, depending on distance.
• Two SCVs on one mineral patch harvest 78-90 minerals per game minute, depending on distance.
• Three SCVs on one mineral patch harvest ~102 minerals per game minute.

Gas is similarly influenced:

• One SCV on gas harvests 33-42 gas per game minute, depending on distance.
• Two SCVs on gas harvest 67-84 gas per game minute, depending on distance.
• Three SCVs on gas harvest 101-114 gas per game minute, depending on distance. In the case of far-diagonal gas placement you will need 4 SCVs for full saturation

You'll notice that going from 1->2 per patch is a significant increase in gain, but 2->3 is less so.

A longer explanation of how to fully saturate can be found here: Whats the correct number of workers to put on gathering vespene and minerals in?

It is also worth noting that when you expand should not be determined by how long it takes a base to mine out, but rather when you are capable of doing so. This usually requires map control.