Calipers would be accurate, a micrometer would probably be most accurate. there's a few options, depends on your purpose.
What do you want to measure about the marble? Its diameter, radius, circumference, volume, mass, density...?
I would use a micrometer. A caliper would do as well.
14mm
A caliper, specifically a digital or vernier caliper, would be the most appropriate instrument to measure the diameter of a marble. It allows for precise measurement of small dimensions and can easily accommodate the curved surface of the marble. Alternatively, a micrometer could also be used for even more precise measurements, although it is less commonly employed for round objects like marbles.
That depends a lot what you want to measure: its diameter, surface area, volume, mass, density, color, hardness, etc.
What do you want to measure about the marble? Its diameter, radius, circumference, volume, mass, density...?
milimetersMilliliter
millimetres or mm
That depends what aspect of a marble you want to measure, for example its diameter, its mass, its density, its color, etc.
That depends what you want to measure: its diameter, its mass, its weight, its color, etc.
I would use a micrometer. A caliper would do as well.
If you have calibrated eyeballs
To determine the size of a single marble, you can measure its diameter using a caliper or ruler. If the marble is spherical, you can also calculate its volume by measuring its diameter, applying the formula for the volume of a sphere (V = 4/3 × π × r³, where r is the radius). Additionally, you can weigh the marble and use its density to find its volume, which can then be related back to its size.
14mm
A caliper, specifically a digital or vernier caliper, would be the most appropriate instrument to measure the diameter of a marble. It allows for precise measurement of small dimensions and can easily accommodate the curved surface of the marble. Alternatively, a micrometer could also be used for even more precise measurements, although it is less commonly employed for round objects like marbles.
6.5cm
That depends a lot what you want to measure: its diameter, surface area, volume, mass, density, color, hardness, etc.