Generally, in English, you may pronounce the plus-minus sign (
by saying "plus or minus".
Generally, you should not say "plus minus".
You do not need to know other details.
In some places, you may find that others say simply "plus minus". In other places, those who work with you may find it strange to hear this pronunciation. There is no universal rule. Generally, you should say "plus or minus", unless you discover that others in some place say "plus minus". Then, you might say either, as long as you remain in the same place.
American English has a rule that British English does not have.
In American English, the way to pronounce a plus-minus sign depends on where the sign appears in a mathematical expression or numerical quantity.
- If the sign appears between two terms in an expression,
then the meaning is the plus operation (addition) or minus operation (subtraction). In this case, the pronunciation is the same as in British English, "plus or minus".
- If the symbol appears before a confidence interval in the numeral part of a quantity, then too the pronunciation is "plus or minus".
- If the symbol appears before the first term in an expression, then the meaning is that the term is positive or negative. In this case, the pronunciation is "positive or negative".
Canadians also follow the rule, as may those in other places that are affected more by American standards than by British. Schools in those countries teach this rule to children.
In practice, Americans and Canadians working in mathematics, science, and engineering often say "plus or minus", for convenience, the same as British, instead of "positive or negative". Some may choose, at certain times, to follow the rule for saying "positive or negative".