How ml to grams conversion actually works
Milliliters measure volume (how much space something takes up); grams measure mass (how much it weighs). These are only interchangeable once you know the substance's density, because 1 mL of a light, airy ingredient like flour weighs far less than 1 mL of a dense liquid like honey. The formula is simple: grams = milliliters × density (g/mL). Water is the reference point, with a density of 1.00 g/mL near room temperature, which is why "1 mL of water = 1 gram" is the one conversion that's always exact.
Why the ratio isn't always 1:1
Once you move away from water, the ratio shifts because different ingredients pack differently at the molecular and structural level. Flour is full of air pockets between fine particles, so it's much lighter than the same volume of water. Honey is a dense sugar solution with very little air or water content, so it's noticeably heavier than water at the same volume. Oils sit slightly below water's density because fat molecules pack a bit less tightly than water molecules.
Reference densities for common ingredients
- Water: 1.00 g/mL — so 250 mL = 250 g
- Whole milk: about 1.03 g/mL — so 250 mL ≈ 258 g
- All-purpose flour (spooned and leveled): about 0.53 g/mL — so 250 mL ≈ 133 g
- Granulated sugar: about 0.85 g/mL — so 250 mL ≈ 213 g
- Powdered (icing) sugar: about 0.56 g/mL — so 250 mL ≈ 140 g
- Brown sugar, packed: about 0.93 g/mL — so 250 mL ≈ 233 g
- Honey: about 1.42 g/mL — so 250 mL ≈ 355 g
- Vegetable oil: about 0.92 g/mL — so 250 mL ≈ 230 g
- Butter, melted: about 0.91 g/mL — so 250 mL ≈ 228 g
- Table salt: about 1.20 g/mL — so 250 mL ≈ 300 g
Why these values are approximate, not universal constants
Unlike water's density, ingredient densities in cooking are practical averages, not physical constants. Flour density depends heavily on whether it was sifted, spooned into the cup, or scooped and packed down — scooped flour can weigh 15-20% more than spooned flour for the same volume. Brown sugar depends on how firmly it's packed. Honey's density varies slightly by floral source and moisture content, and it also thins slightly when warm. Treat the values above as reliable working averages for home cooking and recipe conversion, not laboratory-grade constants.
Accuracy tips
- For baking, weigh ingredients on a kitchen scale whenever possible — it removes the packing-density guesswork entirely.
- Zero (tare) your scale between additions when weighing multiple ingredients into the same bowl.
- For very small volumes (a teaspoon or less), a scale's precision may not help much — precise volume measurement (measuring spoons) is often more practical.
- If a recipe gives weight in grams already, you don't need this conversion at all — measuring by weight is always more accurate than converting from volume.