# the **diameter** of two ropes VS the **diameters** of two ropes

1. The experiment is designed to measure the diameter of two ropes
2. The experiment is designed to measure the diameters of two ropes

Since there are more than one ropes, I am wondering the form of "diameter", single or plural.

PS: I need to say the ropes can have the same size or not.

• Commented Feb 14, 2019 at 15:32

Generally speaking,for measurements, words such as height, weight, length, diameter etc. do not require the plural.

The diameter of the two ropes or two ropes. The length of the chests. The weight of the whales.

However, if you are making a general statement about diameters, you would use the plural.

Diameters of pipes are not easy to measure.

But: The diameter of those pipes is engraved into them.

Just one example:

Sizing Pipes The diameter of the pipes in the irrigation design, along with the size of the valves and system components, has a direct effect on the pressure and velocity of the water moving through the system, which, in turn, affects the performance of the outlets and the longevity of the pipes and other components. As pipes are placed in the design, they are automatically sized based on velocity, if the Min Diameter Not Exceeding Velocity Limit option is selected.diameter of the pipes

You would not generally use the plural unless you were indicating that the diameters are potentially different. Even then it would often be singular, in actual practice.

The experiment is designed to measure the diameter of a rope sample.

If you state there are two ropes, then there should be only two, but you state that there are more than two.

Unless, you mean to say that the experiment measures the difference in diameter between two rope samples.

• Sorry, I was intended to say " more than one". Really sorry again. I have changed the post Commented Feb 14, 2019 at 15:10