A recipe asks for 200 grams and the cupboard has no scale. There are four honest ways out, and they are not equally good.
Measure by volume and convert
Flour, sugar and rice have known weights per cup, and a measuring cup costs nothing. The catch is packing: a cup of flour spooned in loosely and a cup scooped straight from the bag differ by a fifth.
Compare against something of known weight
A litre of water is a kilogram. A standard bag of sugar is a kilogram. Anything you can balance against a known weight gives you a real answer rather than a guess.
Count instead of weighing
Where the recipe means “two apples”, counting beats weighing. Produce sold by the piece is fairly consistent within a size grade.
Photograph it
An estimate from a photograph gets the object named and sized without touching it. It is the fastest of the four and the least precise — useful when you need a figure, not when the figure has to hold up.