No scale in reach, and a number is still needed. Four methods get close, and each one fails in a different, predictable way.
Compare against something of known weight
A litre of water weighs exactly one kilogram, and a one-kilogram bag of sugar does the same job without a jug. Balance the unknown object against one or more of these on a ruler resting across a pencil; a level balance means the two sides are equal. The result is only ever “close to” a known weight, not a number between two — and it fails outright once the object is far outside that weight class, whether that is a lighter at 21 grams or a watermelon in the kilograms.
Convert from a volume you can measure
A measuring cup becomes a scale once the density of what fills it is known: a level cup of flour, spooned in rather than scooped, weighs about 125 grams. Water converts even more directly — a millilitre weighs almost exactly a gram. The method lives or dies on packing: scoop the same cup straight through the bag instead of spooning it in, and the total climbs to around 150 grams from compaction alone, a fifth more flour from the same cup.
Count instead of weighing
Where the question really means “a few of these,” counting skips weighing altogether. A large egg is graded to sit within a few grams of every other large egg, about 57 grams in the shell, and a medium potato runs close to 170 grams — both narrow enough bands that counting gives a workable total. It falls apart the moment the item is not sold to a narrow size: a watermelon runs anywhere from 4 to 11 kilograms, so “one watermelon” is not a weight, it is a guess with no lower bound.
Estimate from a photograph
A photograph gives a number without touching the object: point a camera at it, and software judges size and material from what is in frame. It is the fastest of the four methods and the least precise, since nothing in the shot is a physical measurement unless a reference object was deliberately placed beside it. That trade-off is why a photograph belongs last on this list, not first — good for a quick figure, not for one that has to hold up.