Each bus company in Spain has its own baggage policy, including the maximum weight allowed for checked in and carry-on baggage.
Overall, the norm is for 1 checked in piece of baggage weighing no more than 25kg and 1 standard sized carry-on. Additional baggage can be brought on board for a fee and must be paid for at the station.
Here are the limits for popular bus companies on Busbud:
Alsa: 30 kgs per person in Spain and 25 Kg on international routes
Linebus: 30kgs per person checked in.
Hife: 15kgs per person checked in
If you're travelling with a bus company not listed above, please also check your ticket to see what the baggage limit is.