Bicycle Mechanics - How do I tell if my chain is too long?

I installed a new bike chain. It seems to fit find. But I do not know if my chain is too long. Without having to break a link, can you tell me how to check whether it is in a optimal length?
When the chain is on the largest FD and smallest RD, the rear wheelies (what do you call them?) are above one another rather than parallel. Anyhow, any guidance would be appreciated. What happens if it is too long? It is my commuter bike. Any danger?

Shift to small in front and small on the rear. If the chain is slack or the bottom side chain hits the jockey pulley (the upper one), it is too long.

As supplied in the pack, a new chain is usually too long, although this doesn't deter some manufacturers from fitting them that way. An excessively long chain may skip, causing horrendous wear both to itself and, sometimes, the rear sprockets (for thus are they termed). A skipping chain is dangerous, becuse it tends to skip when the most force is applied to it, which is likely to be the rider standing on the pedals. If it skips when you're not seated, you may end up on your ear. Sheldon, whose wisdom is rightly legendary, recommends threading a new chain around the largest chainwheel in front and the largest sprocket in back (missing out the derailleur), then finding the point at which the chain could, theoretically, be joined, and adding another full link, removing any excess links. A "link" for this purpose is a set of side plates, an inside part and three rivets, one inch long from the first rivet centre to the third one. Other authorities differ, and would have you add two links. You pays your money.....

The big/big plus 1 inch method suggest the shortest possible chain length. Use that method with a 12-23 and later change to a 12-27. The chain will be 1 inch too short for the 12-27.

The little/little method produces the longest possible chain that will work with any cassette within the RD's wrap capacity. Use that length and you'll never have to shorten or lengthen a chain.

Shift to small in front and small on the rear. If the chain is slack or the bottom side chain hits the jockey pulley (the upper one), it is too long.

Apart from test rides, I don't know if I will ever in reality run small small configuration. But I can check it out.

I commuted with the bike today. Didn't feel any skipping. But I stayed with largest front most of the time while modulating b/t the smallest to mid rear cogs along the way.

Apart from test rides, I don't know if I will ever in reality run small small configuration. But I can check it out.

I commuted with the bike today. Didn't feel any skipping. But I stayed with largest front most of the time while modulating b/t the smallest to mid rear cogs along the way.

You're never supposed to use this combination, but you still don't want the chain hanging loose or rubbing. Shifting up one cog is only 1-tooth on most bikes and that takes up a measly 1/4 inch of chain length. It takes 4 teeth to take up 1 inch and 1 inch is the minimum increment of change with a derailleur chain.