Correct tapping speeds are very important in obtaining efficient tapping results. There are many factors which affect tapping speeds, some of which are listed below: 

Material Factors:  
Thermo-conductivity of the material and wall thickness as it affects heat dispersion.
Variations in carbon content of steel.
Hard spots in material.
Depth of hole to be tapped.
Percentage of full thread to be tapped.

Tap Factors:

Major diameters, pitch and lead.

Style of tap.

Width of lands.

Amount of hook or rake.

Length of chamfer. Bottoming taps normally require slower speeds than plug chamfered taps.

Mechanical Factors:

Type of tapping machine and holder; Speeds for small diameter taps are often governed by the limitation of the machine.

Condition of tapping machine and spindle.

Type of fixture.

Vertical or horizontal tapping (faster speeds for vertical tapping).

Method of feeding the tap.

Cutting fluid used and method of application.

RPM =(3.82 x SFM)/D              SFM = .26 x RPM x D

 

Table 327 - Conversion Table (Surface feet per minute to revolutions per minute)
		Surface Feed Per Minute
Tap Sizes		5'	10'	15'	20'	25'	30'	40'	50'	60'	70'	80'	90'	100'	110'	120'	130'	140'	150'
UNC/UNF	Pipe	Revolutions Per Minute
0 1 2 3 4	– – – – –	318 273 212 191 174	637 546 424 382 347	955 819 637 573 521	1273 1046 888 772 682	1592 1308 1110 964 853	1910 1570 1333 1157 1023	2546 2093 1777 1543 1364	3183 2617 2221 1929 1705	3820 3140 2665 2315 2046	4456 3663 3109 2701 2387	5093 4186 3554 3086 2728	5729 4710 3999 3472 3069	6366 5233 4442 3858 3411	7003 5756 4886 4244 3751	7639 6279 5330 4629 4092	8276 6805 5774 5015 4434	8913 7326 6218 5401 4775	9549 7849 6662 5787 5116
5 6 8 10 12	– – – – –	147 136 119 101 87	294 273 239 201 174	441 409 358 302 260	611 553 466 402 354	764 691 583 502 442	917 829 699 603 531	1222 1106 932 804 707	1528 1382 1165 1005 884	1833 1659 1398 1205 1061	2139 1935 1631 1406 1238	2445 2212 1864 1607 1415	2750 2488 2097 1808 1592	3056 2766 2330 2009 1769	3361 3042 2563 2210 1945	3667 3318 2796 2411 2122	3973 3595 3029 2612 2300	4278 3871 3262 2813 2476	4584 4148 3495 3014 2653
1/4 5/16 3/8 7/16 1/2	– – – 1/8 –	76 62 50 43 38	153 123 101 87 76	229 185 151 130 115	306 245 204 175 153	382 306 255 219 191	458 367 305 262 229	611 489 407 349 305	764 611 509 437 382	917 733 611 524 458	1070 856 713 611 535	1222 978 815 698 611	1375 1100 917 786 688	1528 1222 1019 873 764	1681 1345 1120 960 840	1833 1467 1222 1048 917	1986 1589 1324 1135 993	2139 1711 1426 1222 1070	2292 1833 1528 1310 1146
9/16 5/8 11/16 3/4 7/8	1/4 – 3/8 – 1/2	34 32 28 25 22	68 64 55 51 43	102 96 83 76 65	137 122 111 102 87	172 153 138 128 109	206 183 167 153 131	274 244 222 203 175	342 306 278 255 218	410 367 333 305 262	478 428 389 357 306	547 489 444 407 350	616 550 500 458 392	683 611 556 509 437	752 672 611 560 480	820 733 667 611 524	888 794 722 662 568	952 856 778 713 611	1020 917 833 764 655
1 1 1/8 1 1/4 1 3/8 1 1/2	– 3/4 – 1 –	19 17 15 14 13	38 34 31 28 25	57 51 46 42 38	76 68 61 56 51	96 84 76 69 63	115 102 92 83 76	153 136 122 111 102	191 170 153 139 127	230 204 183 167 153	268 238 214 194 178	305 272 244 222 204	344 306 275 250 229	382 340 305 278 255	420 373 336 306 280	458 407 367 333 305	497 441 397 361 331	535 475 428 389 356	573 509 458 417 382
1 5/8 1 3/4 1 7/8 2	– – – –	12 11 10 9	23 22 20 19	35 33 30 29	47 44 41 38	59 55 51 48	71 65 61 57	94 87 81 76	118 109 102 96	141 131 122 115	165 153 143 134	188 175 163 153	212 196 183 172	235 218 204 191	259 240 224 210	282 262 244 229	306 284 265 248	329 306 285 267	353 327 306 287
		Surface Feed Per Minute
		5'	10'	15'	20'	25'	30'	40'	50'	60'	70'	80'	90'	100'	110'	120'	130'	140'	150'
Taps Metric		Revolutions Per Minute
M 1 M 2 M 3 M 3.5 M 4		490 242 162 138 122	979 484 324 277 243	1469 725 486 415 365	1959 967 647 554 487	2449 1209 809 692 608	2938 1451 971 830 730	3918 1934 1295 1107 973	4897 2418 1619 1384 1217	5877 2901 1942 1661 1460	6856 3385 2266 1938 1703	7836 3868 2590 2214 1946	8815 4352 2914 2491 2190	9795 4835 3237 2768 2433	10774 5319 3561 3045 2676	11754 5803 3885 3322 2920	12733 6286 4208 3599 3163	13713 6770 4532 3875 3406	14692 7253 4856 4152 3650
M 5 M 6 M 7 M 8 M 10		97 81 69 61 48	194 162 138 121 97	291 243 208 182 145	388 324 277 243 194	485 405 346 303 242	582 486 415 364 291	776 647 554 485 388	970 809 692 606 485	1163 971 830 728 582	1357 1133 969 849 679	1551 1295 1107 970 776	1745 1457 1246 1091 873	1939 1619 1384 1213 970	2133 1781 1522 1334 1067	2327 1942 1661 1455 1163	2521 2104 1799 1577 1260	2715 2266 1938 1698 1357	2909 2428 2076 1819 1454
M 12 M 14 M 16 M 18 M 20		40 35 30 27 24	81 69 61 54 49	121 104 91 81 73	162 139 121 108 97	202 173 152 135 121	243 208 182 162 146	324 277 243 216 194	405 347 303 269 243	486 416 364 323 291	567 485 424 377 340	647 555 485 431 388	728 624 546 485 437	809 693 606 539 485	890 763 667 593 534	971 832 728 647 582	1052 901 788 700 631	1133 971 849 754 680	1214 1040 910 808 728
M 22 M 24 M 27 M 30		22 20 18 16	44 40 36 32	66 61 54 49	88 81 72 65	110 101 90 81	132 121 108 97	176 162 144 129	221 202 180 162	265 243 216 194	309 283 252 226	353 323 287 259	397 364 323 291	441 404 359 323	485 445 395 356	529 485 431 388	573 526 467 420	618 566 503 453	662 606 539 485