Weighing liquid ingredients is faster and more accurate than measuring them, and it comes with one piece of physics worth understanding first.
Water Is the Convenient Case
One millilitre of water weighs almost exactly one gram at ordinary temperatures. A litre is a kilogram.
That relationship is why metric recipes can list water in either grams or millilitres interchangeably, and it is genuinely convenient.
Weighing Is Still Better
Despite the complication, weighing liquids beats measuring them for most purposes.
A measuring jug is read at eye level against a curved meniscus, it leaves residue behind, and it is another item to wash. Weighing directly into the bowl using tare avoids all of that.
Scales with a tare function and a stable platform for a jug, of the kind across the escali scale range, make this the faster method as well as the more accurate one.
Everything Else Has Its Own Density
The moment the liquid is not water, the relationship changes.
- Milk is slightly denser than water, at roughly 1.03 grams per millilitre
- Oil is lighter, around 0.92, so 100 millilitres weighs about 92 grams
- Honey and syrups are much denser, around 1.4
- Cream, spirits and stock all differ from water and from each other
- Density also changes with temperature
That is why a recipe listing oil in grams and one listing it in millilitres are asking for different amounts, and why following the unit written rather than converting casually matters.
Sticky Liquids Especially
Honey, treacle, golden syrup and condensed milk are where weighing wins outright.
A measuring spoon of honey leaves a substantial proportion behind. Weighed straight into the bowl, none of it is lost and nothing needs scraping.
Fluid Ounces Are Not Ounces
The confusion worth naming. A fluid ounce is a unit of volume; an ounce is a unit of weight. They are different things that share a word.
They coincide for water by rough coincidence in the imperial system and not otherwise. A recipe calling for eight fluid ounces of oil does not want eight ounces of oil.
Worse, an American fluid ounce and a British fluid ounce are not the same size, which catches out anyone using recipes from both.
Temperature
Liquids expand as they warm, so volume changes with temperature while weight does not.
This is a small effect in cooking and a real argument for weight over volume in anything precise, particularly with warm liquids in bread making.
Practical Approach
Follow the unit the recipe uses. Where a recipe gives both, prefer the weight.
Where you are converting an old volume recipe permanently, weigh what you currently use and record the result rather than looking up a table.