A catheter meter is described for determining spacial parameters such as linear distance in a vessel or other body cavity. The catheter meter includes a catheter having a proximal end and a distal end and a handle for holding the catheter. The catheter further includes a hollow tubular member defining a lumen extending distally of the handle to a catheter tip. A wall in the catheter defines a passageway communicating with the lumen for passing a cylindrical member such as a tube or cable having a length and a tip through the passageway and the lumen so that the tip of the cylindrical member can extend distally of the catheter tip. A measurement gauge at the proximal end of the catheter is provided for measuring the distance from the proximal end of the catheter to the tip of the cylindrical member when the tip has been passed through the catheter passageway and the lumen and beyond the catheter tip.