Is it wall moulding or molding?

Both spellings—moulding and molding—are considered correct and acceptable, but their usage is primarily determined by geographical spelling conventions and regional preferences within the English-speaking world. Moulding with the letter u is the traditional spelling standard utilized throughout the United Kingdom, Australia, New Zealand, Canada, and other regions adhering to British Commonwealth English standards. Conversely, molding without the u is the standard spelling utilized widely across the United States in American English dictionaries, architectural literature, and building supply industries. Regardless of which spelling is chosen, both terms refer to the exact same architectural millwork, decorative trim profiles, and manufacturing shaping processes, meaning that homeowners and contractors will understand either variation completely, though matching local publishing or construction conventions is always recommended for professional documentation.