SFM to RPM: Calculator, formulas, and Charts

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The cutting tools catalogs or our experience tells us the SFM (Cutting Speed) we need to use for a given application. On the other hand, the CNC machine is programmed with the RPM (Spindle speed). Therefore it is common that we need to compute the RPM from a given SFM either for programming or to ensure that the SFM we want to run at is within the machine’s limit. It is calculated by dividing the cutting speed by the cutter’s circumference.

SFM to RPM Formula

d – [Inch] (Diameter)
n – [RPM] (Revolutions per minute)
Vc – [SFM] (Surface feet per minute)

\( \large RPM = \huge \frac{12 \times SFM}{\pi \times d} \)

SFM to RPM Calculator

The cutting tools catalogs or our experience tells us the SFM (Cutting Speed) we need to use for a given application. On the other hand, the CNC machine is programmed with the RPM (Spindle speed). Therefore it is common that we need to compute the RPM from a given SFM either for programming or to ensure that the SFM we want to run at is within the machine’s limit. It is calculated by dividing the cutting speed by the cutter’s circumference.

SFM to RPM Chart (Inch)

Find the required RPM according to your tool’s diameter and SFM

SFM	1/16"	1/8"	3/16"	1/4"	3/8"	1/2"	5/8"	3/4"	7/8"	1"	1-1/2"	2"
10	610	305	205	155	100	75	60	50	45	40	25	20
15	915	460	305	230	155	115	90	75	65	55	40	30
20	1,220	610	405	305	205	155	120	100	85	75	50	40
25	1,530	765	510	380	255	190	155	125	110	95	65	50
30	1,835	915	610	460	305	230	185	155	130	115	75	55
35	2,140	1,070	715	535	355	265	215	180	155	135	90	65
40	2,445	1,220	815	610	405	305	245	205	175	155	100	75
45	2,750	1,375	915	690	460	345	275	230	195	170	115	85
50	3,055	1,530	1,020	765	510	380	305	255	220	190	125	95
60	3,665	1,835	1,220	915	610	460	365	305	260	230	155	115
70	4,280	2,140	1,425	1,070	715	535	430	355	305	265	180	135
80	4,890	2,445	1,630	1,220	815	610	490	405	350	305	205	155
90	5,500	2,750	1,835	1,375	915	690	550	460	395	345	230	170
100	6,110	3,055	2,035	1,530	1,020	765	610	510	435	380	255	190
110	6,725	3,360	2,240	1,680	1,120	840	670	560	480	420	280	210
120	7,335	3,665	2,445	1,835	1,220	915	735	610	525	460	305	230
130	7,945	3,975	2,650	1,985	1,325	995	795	660	570	495	330	250
140	8,555	4,280	2,850	2,140	1,425	1,070	855	715	610	535	355	265
150	9,170	4,585	3,055	2,290	1,530	1,145	915	765	655	575	380	285
175	10,695	5,350	3,565	2,675	1,785	1,335	1,070	890	765	670	445	335
200	12,225	6,110	4,075	3,055	2,035	1,530	1,220	1,020	875	765	510	380
225	13,750	6,875	4,585	3,440	2,290	1,720	1,375	1,145	980	860	575	430
250	15,280	7,640	5,095	3,820	2,545	1,910	1,530	1,275	1,090	955	635	480
275	16,810	8,405	5,605	4,200	2,800	2,100	1,680	1,400	1,200	1,050	700	525
300	18,335	9,170	6,110	4,585	3,055	2,290	1,835	1,530	1,310	1,145	765	575
350	21,390	10,695	7,130	5,350	3,565	2,675	2,140	1,785	1,530	1,335	890	670
400	24,450	12,225	8,150	6,110	4,075	3,055	2,445	2,035	1,745	1,530	1,020	765
450	27,505	13,750	9,170	6,875	4,585	3,440	2,750	2,290	1,965	1,720	1,145	860
500	30,560	15,280	10,185	7,640	5,095	3,820	3,055	2,545	2,185	1,910	1,275	955
550	33,615	16,810	11,205	8,405	5,605	4,200	3,360	2,800	2,400	2,100	1,400	1,050
600	36,670	18,335	12,225	9,170	6,110	4,585	3,665	3,055	2,620	2,290	1,530	1,145
700	42,785	21,390	14,260	10,695	7,130	5,350	4,280	3,565	3,055	2,675	1,785	1,335
800	48,895	24,450	16,300	12,225	8,150	6,110	4,890	4,075	3,495	3,055	2,035	1,530
900	55,010	27,505	18,335	13,750	9,170	6,875	5,500	4,585	3,930	3,440	2,290	1,720
1,000	61,120	30,560	20,375	15,280	10,185	7,640	6,110	5,095	4,365	3,820	2,545	1,910
1,250	76,400	38,200	25,465	19,100	12,735	9,550	7,640	6,365	5,455	4,775	3,185	2,390
1,500	91,680	45,840	30,560	22,920	15,280	11,460	9,170	7,640	6,550	5,730	3,820	2,865
1,750	106,960	53,480	35,655	26,740	17,825	13,370	10,695	8,915	7,640	6,685	4,455	3,345
2,000	122,240	61,120	40,745	30,560	20,375	15,280	12,225	10,185	8,730	7,640	5,095	3,820

SFM to RPM Chart (Metric)

Find the required RPM according to your tool’s diameter and SFM

SFM	2 mm	3 mm	4 mm	6 mm	8 mm	10 mm	12 mm	16 mm	20 mm	25 mm	40 mm	50 mm
10	485	325	245	160	120	95	80	60	50	40	25	20
15	730	485	365	245	180	145	120	90	75	60	35	30
20	970	645	485	325	245	195	160	120	95	80	50	40
25	1,215	810	605	405	305	245	200	150	120	95	60	50
30	1,455	970	730	485	365	290	245	180	145	115	75	60
35	1,700	1,130	850	565	425	340	285	210	170	135	85	70
40	1,940	1,295	970	645	485	390	325	245	195	155	95	80
45	2,185	1,455	1,090	730	545	435	365	275	220	175	110	85
50	2,425	1,615	1,215	810	605	485	405	305	245	195	120	95
60	2,910	1,940	1,455	970	730	580	485	365	290	235	145	115
70	3,395	2,265	1,700	1,130	850	680	565	425	340	270	170	135
80	3,880	2,585	1,940	1,295	970	775	645	485	390	310	195	155
90	4,365	2,910	2,185	1,455	1,090	875	730	545	435	350	220	175
100	4,850	3,235	2,425	1,615	1,215	970	810	605	485	390	245	195
110	5,335	3,560	2,670	1,780	1,335	1,065	890	665	535	425	265	215
120	5,820	3,880	2,910	1,940	1,455	1,165	970	730	580	465	290	235
130	6,305	4,205	3,155	2,100	1,575	1,260	1,050	790	630	505	315	250
140	6,790	4,530	3,395	2,265	1,700	1,360	1,130	850	680	545	340	270
150	7,275	4,850	3,640	2,425	1,820	1,455	1,215	910	730	580	365	290
175	8,490	5,660	4,245	2,830	2,120	1,700	1,415	1,060	850	680	425	340
200	9,705	6,470	4,850	3,235	2,425	1,940	1,615	1,215	970	775	485	390
225	10,915	7,275	5,460	3,640	2,730	2,185	1,820	1,365	1,090	875	545	435
250	12,130	8,085	6,065	4,045	3,030	2,425	2,020	1,515	1,215	970	605	485
275	13,340	8,895	6,670	4,445	3,335	2,670	2,225	1,670	1,335	1,065	665	535
300	14,555	9,705	7,275	4,850	3,640	2,910	2,425	1,820	1,455	1,165	730	580
350	16,980	11,320	8,490	5,660	4,245	3,395	2,830	2,120	1,700	1,360	850	680
400	19,405	12,935	9,705	6,470	4,850	3,880	3,235	2,425	1,940	1,550	970	775
450	21,830	14,555	10,915	7,275	5,460	4,365	3,640	2,730	2,185	1,745	1,090	875
500	24,255	16,170	12,130	8,085	6,065	4,850	4,045	3,030	2,425	1,940	1,215	970
550	26,685	17,790	13,340	8,895	6,670	5,335	4,445	3,335	2,670	2,135	1,335	1,065
600	29,110	19,405	14,555	9,705	7,275	5,820	4,850	3,640	2,910	2,330	1,455	1,165
700	33,960	22,640	16,980	11,320	8,490	6,790	5,660	4,245	3,395	2,715	1,700	1,360
800	38,810	25,875	19,405	12,935	9,705	7,760	6,470	4,850	3,880	3,105	1,940	1,550
900	43,665	29,110	21,830	14,555	10,915	8,735	7,275	5,460	4,365	3,495	2,185	1,745
1,000	48,515	32,345	24,255	16,170	12,130	9,705	8,085	6,065	4,850	3,880	2,425	1,940
1,250	60,645	40,430	30,320	20,215	15,160	12,130	10,105	7,580	6,065	4,850	3,030	2,425
1,500	72,770	48,515	36,385	24,255	18,195	14,555	12,130	9,095	7,275	5,820	3,640	2,910
1,750	84,900	56,600	42,450	28,300	21,225	16,980	14,150	10,610	8,490	6,790	4,245	3,395
2,000	97,030	64,685	48,515	32,345	24,255	19,405	16,170	12,130	9,705	7,760	4,850	3,880

Related Glossary Terms: