Which sentence (or sentences) is/are correct?

1) The length of A and B was measured

2) The length of A and B were measured

3) The lengths of A and B were measured

(Suppose both A and B are two separate lines)

  • 2) is obviously wrong, the others depend on what A and B are. If they are separate entities, then use the plural forms. If they are parts of the same object, perhaps the singular, for example when they are segments of the same line. With a slight change, it becomes ambiguous: "The weight of A and B was measured" could refer to their combined weight. Commented Mar 2, 2020 at 21:34
  • @WeatherVane I don't see why two different segments of the same line would be considered to be the same line. Even if both lines, segments of lines, pieces of wood, lengths of wire, stretches of road or anything else were of the same length they would still be different entities. The only time more than one item would have the same length would be if they were made on the same machine. For instance "The length of the pencils was 20cms". You'd determine this by measuring one pencil or measuring the box.
    – BoldBen
    Commented Mar 2, 2020 at 21:47

1 Answer 1


1) This is correct if you mean the length of A + B was measured—as if the two lines were laid end-to-end, then measured for one length in total.

2) This doesn't work.

3) Does A have more than one length? Does B? For lines, that would be impossible I think. This is the old "they nodded their heads/they nodded their head" problem. Does each person have more than head? Do many people share one head? No matter, this construction is widely considered understandable by context. See What Is Subject-Complement Agreement?.

Meanwhile, you can always reword . . . Assuming that A was measured and B was measured, try: A and B were each measured for length.

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