A couple questions from a beginner...

Best you can do is get an estimate of the original Gravity using the Mead Calculator linked over on the left.

There's a few ways to find out the alcohol content after fermentation is complete, but I've never done them.

Well, if you paid attention to your alcohol potential when you made the must, you can figure out a rough equivilent to whatever your starting gravity would have been.

atothestrong said:

Well, if you paid attention to your alcohol potential when you made the must, you can figure out a rough equivilent to whatever your starting gravity would have been.

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Well, since Alcohol Potential is determined by the amount of fermentable sugars in the must and that is determined by either Gravity or Brix which require a Hydrometer or refractometer (don't work very well in Mead musts) reading and he forgot to take a reading it would be kind of hard to pay attention to his Alcohol Potential. The best he can get until the mead is finished is an estimate based on the calculator here or one on another site, but again that is an estimate only.

TAKeyser said:

refractometer (don't work very well in Mead musts)

Click to expand...

Refractometers work fine in mead musts, I was thinking of Vinometers when I was typing.

If you used only honey, still have the jar and remember exactly the weight used it should be trivial. Compute the gravity of honey by dividing the honey's weight by jar's volume. Then compute the water's volume: it's the final volume minus the honey's (=jar's) one. Then make a weighted average.

So, if you used 1 kg honey from a 0.7 l jar, then the honey had gravity 1 / 0.7 = 1.429.
Final volume was 5 l, so you added 5 - 0.7 = 4.3 l water.
O.G. is then (honey_gravity * honey_volume + water_gravity * water_volume) / final_volume
(1.429 * 0.7 + 4.3) / 5 = 1.060

If you used 2 jars honey, its gravity it's still 1.429, but you added less water:
Final volume was 5 l, so you added 5 - 2*0.7 = 3.6 l water.
O.G. is then (honey_gravity * honey_volume + water_gravity * water_volume) / final_volume
(1.429 * 2*0.7 + 3.6) / 5 = 1.120

Note that water's gravity is exactly 1.

You may also see in this way: gravity = total_weight / total_volume. You already know total_volume, you know honey's weight, you just need to compute water's weight (which is the same as water's volume).

gravity = (honey_weight + water_weight) / (honey_volume + waters_volume) =
= (honey_weight + water_volume) / total_volume
= (honey_weight + (total_volume - honey_volume)) / total_volume

This proves very useful when you use BDCDYF technique.
If you had other fermentables in your must things gets more complicate. If you used juices you can still do the weight / volume trick, otherwise not (but even an hydrometer wouldn't help you there).

By the way the mead calculator does exactly these computations, but it uses its own honey's gravity, which is imprecise if you use weird honey (very liquid or very solid).