It's 8 tablespoons.
One standard US stick of butter = 8 tablespoons = ½ cup = 4 ounces = 113 grams. That's it. You can stop reading now if that's all you came for.
Still here? Good, because the moment you need anything other than one whole stick, it gets annoying fast. Here's the rest.
The quick butter chart
½ stick = 4 tbsp = ¼ cup = 2 oz = 57 g
1 stick = 8 tbsp = ½ cup = 4 oz = 113 g
2 sticks = 16 tbsp = 1 cup = 8 oz = 227 g
4 sticks = 32 tbsp = 2 cups = 16 oz (1 lb) = 454 g
"My recipe wants 6 tablespoons — how much of a stick is that?"
Three-quarters of a stick. Most US butter wrappers are printed with tablespoon lines, so you can just slice at the mark. No wrapper? Run the number through the DriftSmart Butter Converter and it'll tell you exactly where to cut.
A warning about European butter
If you bought a fancy import (or you're baking from a European recipe), don't assume 8 tablespoons. European butter often comes in 250 g blocks, not 113 g sticks — that's roughly 17.6 tablespoons, more than double a US stick. This is the #1 way recipes get wrecked in translation. When in doubt, convert by weight, not by "sticks."
Why weight beats sticks for baking
Volume measurements drift — how you pack, slice, or soften butter changes the number. Weight doesn't. 113 grams is 113 grams no matter what. If your recipe gives grams and your butter's in sticks (or vice versa), the butter converter handles the swap instantly so your bake actually comes out right.