Yes, the dimensions should be accurate, especially for an inside mount. Blindster will reduce the width by about a quarter of an inch on each side to ensure the blind fits in the space. Because of this, the blind won't be flush to the window frame. It's personal preference about that space. If you think it will bother you, then you should opt for an outside mount. In that case, the dimensions you provide will be the actual dimension of the blind you receive. If you have blinds on the window right now, don't measure the blind, measure the window.