Tables of Critical Values oft for Probabilities
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Critical t Values Commonly Used : df=1 to 100
The table presents the most commonly used critical t values for 1 to 100 degrees of freedom, and for 2 α values (0.1 2 tail;0.05 1 tail, and 0.05 2tail;0.025 one tail).

α is the probability of Type I error.

For example, at 20 degrees of freedom, the t value of 2.086 is critical for α=0.05(2 tail) and α=0.025(1 tail). With the same degrees of frredom, 1.725 is critical for α=0.1(2 tail) and α=0.05(1 tail).

α(1 tail)0.050.0250.050.0250.050.0250.050.0250.050.025
α(2 tail)0.100.0500.100.0500.100.0500.100.0500.100.050
dfdfdfdfdf
16.313812.707211.72072.0796411.68292.0196611.67021.9996811.66391.9897
22.92004.3026221.71722.0739421.68202.0181621.66981.9990821.66361.9893
32.35343.1824231.71392.0686431.68112.0167631.66941.9983831.66341.9889
42.13192.7764241.71092.0639441.68022.0154641.66901.9977841.66321.9886
52.01502.5706251.70812.0596451.67942.0141651.66861.9971851.66301.9883
61.94322.4469261.70562.0555461.67872.0129661.66831.9966861.66281.9879
71.89462.3646271.70332.0518471.67792.0117671.66791.9960871.66261.9876
81.85952.3060281.70112.0484481.67722.0106681.66761.9955881.66231.9873
91.83312.2621291.69912.0452491.67662.0096691.66731.9950891.66221.9870
101.81242.2282301.69732.0423501.67592.0086701.66691.9944901.66201.9867
111.79592.2010311.69552.0395511.67532.0076711.66661.9939911.66181.9864
121.78232.1788321.69392.0369521.67472.0066721.66631.9935921.66161.9861
131.77092.1604331.69242.0345531.67412.0057731.66601.9930931.66141.9858
141.76132.1448341.69092.0322541.67362.0049741.66571.9925941.66121.9855
151.75302.1314351.68962.0301551.67302.0041751.66541.9921951.66101.9852
161.74592.1199361.68832.0281561.67252.0032761.66521.9917961.66091.9850
171.73962.1098371.68712.0262571.67202.0025771.66491.9913971.66071.9847
181.73412.1009381.68592.0244581.67152.0017781.66461.9909981.66061.9845
191.72912.0930391.68492.0227591.67112.0010791.66441.9904991.66041.9842
201.72472.0860401.68392.0211601.67062.0003801.66411.99011001.66021.9840

Critical t Values Complete Table : df = 1 to 200