heating calculation

You're probably doing what most homeowners do at this point. You've found a radiator you like, the size looks about right, the finish suits the room, then the product page throws BTU, Watts, and Delta T at you and the whole thing becomes less certain. That confusion is justified. A lot of online advice still

You've finished decorating the spare room, replaced the carpet, picked the curtains, and then the old radiator starts bothering you. It's either too small and the room never feels comfortable, or it's oversized and dominates the wall for no good reason. That's usually the point where people start searching for a radiator heat output calculator.