One US stick of butter is 1/4 pound (4 oz), which equals 113.398 g exactly using the international avoirdupois pound (1 lb = 453.59237 g, NIST SP 811). Most recipes and labels round this to 113 g or 113.4 g. Each stick also equals 1/2 cup, 8 tablespoons, or 24 teaspoons.

Divide 250 g by 113.398 g per stick: 250 ÷ 113.4 ≈ 2.20 sticks. That's also roughly 1 cup + 1.5 tbsp, or about 17.6 tablespoons. For most recipes, 2 sticks (227 g) plus an extra 1.5 tbsp is close enough; for precision baking, weigh the 250 g directly.

Butter is less dense than water — about 0.911 g/mL at refrigerator temperature, per USDA FoodData Central. A US cup is 236.6 mL, so 236.6 × 0.911 ≈ 215 g if measured as fluid volume. The customary baking value of 227 g (8 oz) treats a cup of butter as 2 sticks by weight, which is the convention US recipes and butter wrappers use.

Yes — melting changes volume slightly (butter expands a little when liquid) but mass is conserved. 113 g of solid butter is still 113 g melted. If a recipe says '1/2 cup melted butter,' measure 113 g on a scale, or measure 1/2 cup solid butter first and then melt it; do not measure 1/2 cup of already-melted butter, which will weigh less.

By weight and volume, yes — both are about 80% butterfat per FDA Food Labeling Regulations (21 CFR 184.1979 for butter standards). Salted butter contains 1.5–2% salt (about 1/4 to 1/3 tsp per stick). If you substitute salted for unsalted in baking, reduce the recipe's added salt by that amount to keep the flavor balanced.

No, the weight-to-volume conversion is the same. US butter is at least 80% butterfat; European-style (Plugrá, Kerrygold, etc.) is typically 82–85%. Density differs by less than 1%, which is invisible at recipe scale. Use the same gram-to-stick conversions; the difference shows up in flavor and texture, not in measurement.