ABSTRACT  Aiming to study the effect of fiber  maturity on fiber  fineness measurements and using HVI micronaire and MR to calculate an estimate value of fiber, perimeter P, diameter D and cross section area ACS compared to image analysis cross section data. Lint cotton samples of three Mike levels from seven Egyptian cotton genotypes representing ELS, Delta and South Egypt LS cottons were tested by HVI, cutter & causticare and Cross section - Image analysis direct methods. The results indicated that mature fibers have bigger P, D and ACS than low mature fibers; the normal mature fibers (medium Mike level) showed calculated perimeter values similar to Image analysis determined ones while the low mature and high mature samples showed biased low and high values. Calculated D was smaller than the large width determined by image analysis, while calculated ACS showed higher values than Image analysis ones. Data of  P, D, and ACS obtained from Applying Lord equation to HVI Mike and MR were more accurate and reliable than those obtained from using Mike* 39.37 to calculate these parameters. Regression equations were developed to make corrections to the calculated data:  Perimeter µ     Y = 4.792 + 0.899x,       Diameter µ       Y = - 2.905 + 1.262x      Area of cross section µ²    Y = 56.192 + 0.591x     ABSTRACT  Aiming to study the effect of fiber  maturity on fiber  fineness measurements and using HVI micronaire and MR to calculate an estimate value of fiber, perimeter P, diameter D and cross section area ACS compared to image analysis cross section data. Lint cotton samples of three Mike levels from seven Egyptian cotton genotypes representing ELS, Delta and South Egypt LS cottons were tested by HVI, cutter & causticare and Cross section - Image analysis direct methods. The results indicated that mature fibers have bigger P, D and ACS than low mature fibers; the normal mature fibers (medium Mike level) showed calculated perimeter values similar to Image analysis determined ones while the low mature and high mature samples showed biased low and high values. Calculated D was smaller than the large width determined by image analysis, while calculated ACS showed higher values than Image analysis ones. Data of  P, D, and ACS obtained from Applying Lord equation to HVI Mike and MR were more accurate and reliable than those obtained from using Mike* 39.37 to calculate these parameters. Regression equations were developed to make corrections to the calculated data:  Perimeter µ     Y = 4.792 + 0.899x,       Diameter µ       Y = - 2.905 + 1.262x      Area of cross section µ²    Y = 56.192 + 0.591x