How wide does the ventilation hood need to be? This depends firstly on the width of the cooktop and secondly on the size of your kitchen. It is important for the hood to be slightly wider than the cooktop below it. Only then can you be certain of capturing all the rising steam and cooking vapors and benefit fully from the hood's power. If there is not enough space for this, then the hood should be at least as wide as the Cooktop. Non-standard widths of up to 86.6 in are possible for many models.