Aim: Evaluate the influence of instrument size on accuracy of three different apex locators in the presence of different irrigation solutions in vital teeth. Materials and methods: 200 human teeth 1st Molar of upper or lower teeth which were scheduled for root canal therapy from 178 patients aged between 18 to 60 years. Endodontic access cavity was prepared and canals were preflared using sequential Gates Glidden drills (Mani Inc. Japan), and irrigated with any one of the irrigation solution (3% NaOCl or 2% CHX or 17% EDTA solution). Working Length of each canal was estimated by using three different apex locators (Elements, iPex and Root ZX) with (in sequence) with instrument sizes #8, #10 and #15 K files (Dentsply, Maillefer). Later the working length was established by (#15 k file) by Ingle’s method using a Radiovisiograph (RVG) which was 0.5 mm short of the radiographic apex (which was approved by 2 specialists in endodontics) and recorded separately. Results: #15 k files does not showed any significant difference with all the apex locators where as #8 k files showed very high significant difference with all the apex locators. Irrigation solutions did not showed any effect on EAL Conclusion: This present study concludes that all investigated devices and instruments to make shorter rather than longer measurements. #15 k file showed better result than #10 k file and least with #8 k file for all the apex locators. Irrigation solutions and vitality did not affect the accuracy of EAL. Root ZX showed better accuracy than Elements Apex locator and iPex with #10 k file with CHX solution and A higher frequency tendency to make unstable measurements with size 8 instruments. Summary: This present study summarizes that all investigated devices and instruments to make shorter rather than longer measurements.#15 k file showed better result than #10 k file and least with #8 k file for all the apex locators.Irrigation solutions and vitality did not affect the accuracy of EAL. Root ZX showed better accuracy than Elements Apex locator and iPex with #10 k file with CHX solution and A higher frequency tendency to make unstable measurements with size 8 instruments.