Is the word calças the same in Brazilian and European Portuguese?

No.

While the core meaning of the word remains the same, there is a significant difference in grammar and typical usage. In Brazil, it is very common and natural to use the singular form "uma calça" to refer to a single pair of trousers. In Portugal, using the singular to refer to the garment is considered incorrect; one must use the plural "umas calças" to refer to even a single pair. Additionally, while Brazilians typically use the term "calça jeans," Portuguese people usually refer to them as "calças de ganga."

Brazilian Portuguese Examples:

1. Eu comprei uma calça nova hoje. (I bought a new pair of pants today.)
2. Essa calça azul é muito bonita. (Those blue pants are very pretty.)
3. Você tem uma calça preta para me emprestar? (Do you have a pair of black pants to lend me?)
4. Eu não gosto de usar calça apertada. (I don't like wearing tight pants.)
5. Onde você comprou essa calça jeans? (Where did you buy those jeans?)

European Portuguese Examples:

1. Eu comprei umas calças novas hoje. (I bought some new trousers today.)
2. Essas calças azuis são muito bonitas. (Those blue trousers are very pretty.)
3. Podes emprestar-me umas calças pretas? (Can you lend me some black trousers?)
4. Eu não gosto de usar calças justas. (I don't like wearing tight trousers.)
5. Onde é que compraste essas calças de ganga? (Where did you buy those jeans?)