Most apple juices/fresh pressed ciders range from 1.030-1.050. If it had an OG of 1.050 you are at about 6.5% ACV.
If it was 1.030, you are looking at 3.9% ACV (assuming ferments to 1.000).
If adding 1 cup granulated sugar to 1 gallon you will raise SG by 0.020 or approx 2.6%, if ferments to 1.000.
Once you hit 7% you fall into wine world, under most standards, so it can take a bit longer for things to age/mesh.