A batch that starts at 1.050 and finishes at 1.010 comes out to 5.25% ABV by the simple homebrew formula and 5.34% ABV by the advanced formula — close enough at this gravity that the choice between them barely matters, but not identical, and the gap is the first thing worth understanding rather than memorising just one number.
The two numbers, and why they're not the same number
(OG - FG) x 131.25 is the formula most homebrewers learn first: (1.050 - 1.010) x 131.25 = 5.25. It's fast, and it's a straight-line approximation of a relationship that isn't actually straight. The advanced formula — (76.08 x (OG - FG) / (1.775 - OG)) x (FG / 0.794) — accounts for how the density of an alcohol/water/extract mixture actually changes as fermentation progresses, and returns 5.34% for the same two readings. At 1.050 OG the two formulas are only about a tenth of a percent apart; that gap widens considerably at higher starting gravities, which is why brewing software increasingly defaults to the advanced version rather than the one most people learned by hand. Run OG 1.050 / FG 1.010 through the ABV calculator to see both side by side along with attenuation and calories.
What else this pair tells you
The same two readings give 80% apparent attenuation — a fairly dry finish, on the higher side of normal for an ale yeast, consistent with a clean, well-attenuating strain and a fermentable wort. Real attenuation (which corrects for the fact that dissolved alcohol makes a hydrometer read artificially low) comes out to roughly 65% for this pair — noticeably lower than the apparent figure, which is completely normal and not a sign anything went wrong; see apparent vs. real attenuation if the gap between those two numbers is what brought you here.
A 12 oz (355 mL) beer at this OG/FG works out to roughly 142 kcal, and a 330 mL serving to roughly 132 kcal, using the same Balling-based estimate the ABV calculator runs — see how many calories are in a homebrew for how that scales with strength.
If your readings are close but not exact
A hydrometer reading a couple of thousandths off from 1.050 or 1.010 won't move the ABV by much — the formula is smooth and forgiving of small measurement error — but it will move it. If your sample was warm or cold when you read it rather than at your hydrometer's calibration temperature, correct it first: see the hydrometer temperature correction chart. A gravity reading taken at 90°F without correction can be off by a couple of points, which is enough to noticeably shift a calculated ABV at the margins.
If your actual OG or FG differs
OG 1.060 to FG 1.012 is the next most common combination this site sees asked about, landing a bit higher in both ABV and attenuation. If your FG came in well above 1.020 relative to a 1.050 OG, that's a different situation — see why is my final gravity stuck at 1.020 for what usually causes an early stall and what to do about it before assuming the batch is finished.