To convert milliliters to grams, multiply the number of milliliters by the density of the substance. For water, the conversion is nearly one-to-one: 1 ml equals roughly 1 gram. For everything else, you need to know the density, because a milliliter of honey weighs far more than a milliliter of oil.
The Formula
Milliliters measure volume. Grams measure mass. The bridge between them is density, which tells you how much mass is packed into a given volume. The formula is straightforward:
Grams = Milliliters × Density (in g/ml)
So if you have 250 ml of a liquid with a density of 1.03 g/ml, you get 250 × 1.03 = 257.5 grams. To go the other direction, divide grams by density to get milliliters.
Why Water Is the Easy One
Pure water has a density of 0.998 g/ml at 20°C and 0.997 g/ml at 25°C. For any practical purpose, 1 ml of water equals 1 gram. This is not a coincidence. The gram was originally defined as the mass of one cubic centimeter (one milliliter) of water, so the two units are historically linked.
This makes water the simplest conversion: 100 ml = 100 grams, 250 ml = 250 grams, and so on. The tiny difference from a perfect 1.000 only matters in laboratory work.
Common Densities for Cooking
Most people searching this are in the kitchen, trying to convert a recipe. Here are the densities that matter most:
- Water: 1.00 g/ml
- Whole milk: 1.03 g/ml
- Skim milk: 1.033 g/ml
- Heavy cream: 0.994 g/ml
- Honey: 1.4 g/ml
- Vegetable and olive oil: 0.91–0.95 g/ml
Notice the pattern. Fatty liquids like oil and cream are lighter than water, so a milliliter weighs less than a gram. Dense, sugary liquids like honey are heavier, so a milliliter weighs more. If you measure 100 ml of honey, you have about 140 grams. Measure 100 ml of olive oil, and you have roughly 92 grams. Treating them all as “1 ml = 1 gram” throws off your recipe by 8% to 40%.
How to Do the Math Quickly
For liquids close to water’s density (milk, juice, vinegar, broth), you can treat milliliters and grams as equal without meaningful error. The density of whole milk is 1.03 g/ml, which means 250 ml of milk weighs 257.5 grams. That’s only 3% off from assuming it weighs 250 grams, and most recipes can absorb that.
For oils, multiply your milliliters by 0.92 as a quick estimate. So 100 ml of oil is about 92 grams. For honey, multiply by 1.4. These numbers don’t need to be exact to the decimal for cooking, but skipping them entirely will change your results.
Dry Ingredients Are Trickier
The ml-to-grams formula works cleanly for liquids because their density stays consistent when you pour them. Dry ingredients are a different story. The density of flour, sugar, or cocoa powder changes dramatically depending on whether the ingredient is sifted, spooned, or scooped.
A cup of all-purpose flour (about 240 ml) weighs 120 grams when spooned gently into the cup, according to King Arthur Baking’s weight chart. But if you dip the cup directly into the flour bag and pack it down, that same cup can weigh as much as 170 grams. That’s a 42% difference from the same volume, which is enough to turn a tender cake into a dense brick. Loose corn starch has a density of only about 0.6 g/ml, meaning 100 ml weighs just 60 grams.
This is exactly why baking recipes increasingly list ingredients by weight. If a recipe gives you milliliters or cups of a dry ingredient, look for a weight chart specific to that ingredient rather than using a single density number.
Temperature Changes the Density Slightly
Liquids expand when they warm up and contract when they cool down. This means a milliliter of cold liquid is slightly heavier than a milliliter of warm liquid. For everyday cooking, this effect is negligible. The density of water shifts by only about 0.1% between 20°C and 25°C.
Over larger temperature swings the change becomes more noticeable. Cryopreservation research shows that some liquid solutions increase in density by about 4% when cooled from 25°C down to roughly -40°C. For kitchen purposes, though, the difference between a cold and room-temperature liquid is well under 1%, and you can safely ignore it.
Why a Kitchen Scale Beats Volume Measuring
If you find yourself regularly converting between milliliters and grams, a digital kitchen scale simplifies everything. Volume measurements using cups and spoons carry significant error. The same single-cup measure of flour can range from 85 grams to 170 grams depending on your scooping technique. A scale eliminates that variability entirely.
One more detail worth noting: a US cup is defined as 240 ml by NIST (the National Institute of Standards and Technology), while an Australian metric cup is 250 ml. If you’re following a recipe from another country, check which cup standard it uses before converting to grams, or the math will be off by about 4% before you even factor in density.