任意の正の数 x は、x = a × 10ˢ （1 ≦ a < 10, s は整数）の形で表せる。したがって、任意の真数 x に対する常用対数 log₁₀ x の値を知りたいときには、log₁₀ x = s + log₁₀ a より、真数が 1 以上 10 未満のときの値から算出することができる。下記の常用対数表は、左の列に真数の小数第1位までが、上の行に真数の小数第2位が書かれている。例えば、log₁₀ 1.23 の値は、1.2 の行と 3 の列を読むことより、約 0.0899 とわかる。数   0     1     2     3     4     5     6     7     8     91.0 .0000 .0043 .0086 .0128 .0170 .0212 .0253 .0294 .0334 .03741.1 .0414 .0453 .0492 .0531 .0569 .0607 .0645 .0682 .0719 .07551.2 .0792 .0828 .0864 .0899 .0934 .0969 .1004 .1038 .1072 .11061.3 .1139 .1173 .1206 .1239 .1271 .1303 .1335 .1367 .1399 .14301.4 .1461 .1492 .1523 .1553 .1584 .1614 .1644 .1673 .1703 .17321.5 .1761 .1790 .1818 .1847 .1875 .1903 .1931 .1959 .1987 .20141.6 .2041 .2068 .2095 .2122 .2148 .2175 .2201 .2227 .2253 .22791.7 .2304 .2330 .2355 .2380 .2405 .2430 .2455 .2480 .2504 .25291.8 .2553 .2577 .2601 .2625 .2648 .2672 .2695 .2718 .2742 .27651.9 .2788 .2810 .2833 .2856 .2878 .2900 .2923 .2945 .2967 .29892.0 .3010 .3032 .3054 .3075 .3096 .3118 .3139 .3160 .3181 .32012.1 .3222 .3243 .3263 .3284 .3304 .3324 .3345 .3365 .3385 .34042.2 .3424 .3444 .3464 .3483 .3502 .3522 .3541 .3560 .3579 .35982.3 .3617 .3636 .3655 .3674 .3692 .3711 .3729 .3747 .3766 .37842.4 .3802 .3820 .3838 .3856 .3874 .3892 .3909 .3927 .3945 .39622.5 .3979 .3997 .4014 .4031 .4048 .4065 .4082 .4099 .4116 .41332.6 .4150 .4166 .4183 .4200 .4216 .4232 .4249 .4265 .4281 .42982.7 .4314 .4330 .4346 .4362 .4378 .4393 .4409 .4425 .4440 .44562.8 .4472 .4487 .4502 .4518 .4533 .4548 .4564 .4579 .4594 .46092.9 .4624 .4639 .4654 .4669 .4683 .4698 .4713 .4728 .4742 .47573.0 .4771 .4786 .4800 .4814 .4829 .4843 .4857 .4871 .4886 .49003.1 .4914 .4928 .4942 .4955 .4969 .4983 .4997 .5011 .5024 .50383.2 .5051 .5065 .5079 .5092 .5105 .5119 .5132 .5145 .5159 .51723.3 .5185 .5198 .5211 .5224 .5237 .5250 .5263 .5276 .5289 .53023.4 .5315 .5328 .5340 .5353 .5366 .5378 .5391 .5403 .5416 .54283.5 .5441 .5453 .5465 .5478 .5490 .5502 .5514 .5527 .5539 .55513.6 .5563 .5575 .5587 .5599 .5611 .5623 .5635 .5647 .5658 .56703.7 .5682 .5694 .5705 .5717 .5729 .5740 .5752 .5763 .5775 .57863.8 .5798 .5809 .5821 .5832 .5843 .5855 .5866 .5877 .5888 .58993.9 .5911 .5922 .5933 .5944 .5955 .5966 .5977 .5988 .5999 .60104.0 .6021 .6031 .6042 .6053 .6064 .6075 .6085 .6096 .6107 .61174.1 .6128 .6138 .6149 .6160 .6170 .6180 .6191 .6201 .6212 .62224.2 .6232 .6243 .6253 .6263 .6274 .6284 .6294 .6304 .6314 .63254.3 .6335 .6345 .6355 .6365 .6375 .6385 .6395 .6405 .6415 .64254.4 .6435 .6444 .6454 .6464 .6474 .6484 .6493 .6503 .6513 .65224.5 .6532 .6542 .6551 .6561 .6571 .6580 .6590 .6599 .6609 .66184.6 .6628 .6637 .6646 .6656 .6665 .6675 .6684 .6693 .6702 .67124.7 .6721 .6730 .6739 .6749 .6758 .6767 .6776 .6785 .6794 .68034.8 .6812 .6821 .6830 .6839 .6848 .6857 .6866 .6875 .6884 .68934.9 .6902 .6911 .6920 .6928 .6937 .6946 .6955 .6964 .6972 .69815.0 .6990 .6998 .7007 .7016 .7024 .7033 .7042 .7050 .7059 .70675.1 .7076 .7084 .7093 .7101 .7110 .7118 .7126 .7135 .7143 .71525.2 .7160 .7168 .7177 .7185 .7193 .7202 .7210 .7218 .7226 .72355.3 .7243 .7251 .7259 .7267 .7275 .7284 .7292 .7300 .7308 .73165.4 .7324 .7332 .7340 .7348 .7356 .7364 .7372 .7380 .7388 .73965.5 .7404 .7412 .7419 .7427 .7435 .7443 .7451 .7459 .7466 .74745.6 .7482 .7490 .7497 .7505 .7513 .7520 .7528 .7536 .7543 .75515.7 .7559 .7566 .7574 .7582 .7589 .7597 .7604 .7612 .7619 .76275.8 .7634 .7642 .7649 .7657 .7664 .7672 .7679 .7686 .7694 .77015.9 .7709 .7716 .7723 .7731 .7738 .7745 .7752 .7760 .7767 .77746.0 .7782 .7789 .7796 .7803 .7810 .7818 .7825 .7832 .7839 .78466.1 .7853 .7860 .7868 .7875 .7882 .7889 .7896 .7903 .7910 .79176.2 .7924 .7931 .7938 .7945 .7952 .7959 .7966 .7973 .7980 .79876.3 .7993 .8000 .8007 .8014 .8021 .8028 .8035 .8041 .8048 .80556.4 .8062 .8069 .8075 .8082 .8089 .8096 .8102 .8109 .8116 .81226.5 .8129 .8136 .8142 .8149 .8156 .8162 .8169 .8176 .8182 .81896.6 .8195 .8202 .8209 .8215 .8222 .8228 .8235 .8241 .8248 .82546.7 .8261 .8267 .8274 .8280 .8287 .8293 .8299 .8306 .8312 .83196.8 .8325 .8331 .8338 .8344 .8351 .8357 .8363 .8370 .8376 .83826.9 .8388 .8395 .8401 .8407 .8414 .8420 .8426 .8432 .8439 .84457.0 .8451 .8457 .8463 .8470 .8476 .8482 .8488 .8494 .8500 .85067.1 .8513 .8519 .8525 .8531 .8537 .8543 .8549 .8555 .8561 .85677.2 .8573 .8579 .8585 .8591 .8597 .8603 .8609 .8615 .8621 .86277.3 .8633 .8639 .8645 .8651 .8657 .8663 .8669 .8675 .8681 .86867.4 .8692 .8698 .8704 .8710 .8716 .8722 .8727 .8733 .8739 .87457.5 .8751 .8756 .8762 .8768 .8774 .8779 .8785 .8791 .8797 .88027.6 .8808 .8814 .8820 .8825 .8831 .8837 .8842 .8848 .8854 .88597.7 .8865 .8871 .8876 .8882 .8887 .8893 .8899 .8904 .8910 .89157.8 .8921 .8927 .8932 .8938 .8943 .8949 .8954 .8960 .8965 .89717.9 .8976 .8982 .8987 .8993 .8998 .9004 .9009 .9015 .9020 .90258.0 .9031 .9036 .9042 .9047 .9053 .9058 .9063 .9069 .9074 .90798.1 .9085 .9090 .9096 .9101 .9106 .9112 .9117 .9122 .9128 .91338.2 .9138 .9143 .9149 .9154 .9159 .9165 .9170 .9175 .9180 .91868.3 .9191 .9196 .9201 .9206 .9212 .9217 .9222 .9227 .9232 .92388.4 .9243 .9248 .9253 .9258 .9263 .9269 .9274 .9279 .9284 .92898.5 .9294 .9299 .9304 .9309 .9315 .9320 .9325 .9330 .9335 .93408.6 .9345 .9350 .9355 .9360 .9365 .9370 .9375 .9380 .9385 .93908.7 .9395 .9400 .9405 .9410 .9415 .9420 .9425 .9430 .9435 .94408.8 .9445 .9450 .9455 .9460 .9465 .9469 .9474 .9479 .9484 .94898.9 .9494 .9499 .9504 .9509 .9513 .9518 .9523 .9528 .9533 .95389.0 .9542 .9547 .9552 .9557 .9562 .9566 .9571 .9576 .9581 .95869.1 .9590 .9595 .9600 .9605 .9609 .9614 .9619 .9624 .9628 .96339.2 .9638 .9643 .9647 .9652 .9657 .9661 .9666 .9671 .9675 .96809.3 .9685 .9689 .9694 .9699 .9703 .9708 .9713 .9717 .9722 .97279.4 .9731 .9736 .9741 .9745 .9750 .9754 .9759 .9763 .9768 .97739.5 .9777 .9782 .9786 .9791 .9795 .9800 .9805 .9809 .9814 .98189.6 .9823 .9827 .9832 .9836 .9841 .9845 .9850 .9854 .9859 .98639.7 .9868 .9872 .9877 .9881 .9886 .9890 .9894 .9899 .9903 .99089.8 .9912 .9917 .9921 .9926 .9930 .9934 .9939 .9943 .9948 .99529.9 .9956 .9961 .9965 .9969 .9974 .9978 .9983 .9987 .9991 .9996