In the midwifery profession, measuring pelvic and cervical dilatation is essential for making decisions, especially when the mother is in labor phase. For this reason, several studies have been conducted in pelvimetry.[1-4] Measurement of the cervix and judgments about pelvic dimensions are performed by the midwife's fingers. However, as finger size and how to measure the distance between the fingers differ from person to person, it is important to develop a method with similar results for everyone. A reliable and convenient tool would thus be advantageous for different fields of medical sciences. The “midwifery ruler” is used to produce homogenous measurements by different obstetricians and midwives. It is a ruler with three blades. Two of them (blades A and B) join together and make a cross. The ends of these two blades are connected to another blade (C). Blade C is mobile and is scaled with centimeters. After entering the ruler into the vagina, the blade edges are placed near the edges of the cervix, the edges are rounded to avoid injury and perforation in vaginal tissue and amniotic membranes. The cervical dilatation is measured by opening the blades. It is also possible to estimate the diameter of the mid-pelvis with the same method. As a third application, this tool can measure diagonal diameter by completely sticking blades A and B and placing one end near promontory of sacra bone while the other end is placed in pubic bone angle. The distance can then be measured by observing the scaled surface.The ruler can be made of durable and sterilized metal or compact plastic (for disposable products). The midwifery ruler has been registered at Invention Registry of Islamic Republic of Iran (No. 389030679) in 2010.