Christy Mathewson has the best career ERA when winning 300+ games, with an ERA of 2.13.

Interpreted as:

lowest era by a pitcher with 300 or more wins

	NAME	ERA	W	L	W%	G	GS	SO	CG	SHO	SV	IP	H	ER	R	HR	BB	HBP	GF	IBB	TBF	WP	K/9	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	ERA-	FIP	FIP-	H/9	PRAA
1	Christy Mathewson C. Mathewson	2.13	373	188	.665	636	552	2,507	435	79	30	4788.2	4,219	1,135	1,620	89	848	59	73		18,913	115	4.71	1.59	2.96	0.17	13.3	4.5	1.06	.268	3.04	75	2.26	76	7.93	363
2	Walter Johnson W. Johnson	2.17	417	279	.599	802	666	3,509	531	110	34	5914.1	4,913	1,424	1,902	97	1,363	205	127		23,405	154	5.34	2.07	2.57	0.15	15.0	5.8	1.06	.264	2.89	68	2.42	76	7.48	472.8
3	Eddie Plank E. Plank	2.35	326	194	.627	623	529	2,246	410	69	23	4495.2	3,958	1,174	1,566	42	1,072	190	77		17,803	88	4.50	2.15	2.10	0.08	12.6	6.0	1.12	.275	3.14	81	2.45	86	7.92	195.2
4	Grover Alexander G. Alexander	2.56	373	208	.642	696	600	2,198	436	90	32	5190.0	4,868	1,476	1,852	165	951	70	81		20,893	38	3.81	1.65	2.31	0.29	10.5	4.6	1.12	.269	3.21	73	2.88	81	8.44	359.1
5	Cy Young C. Young	2.63	511	316	.618	906	815	2,803	749	76	17	7356.0	7,092	2,147	3,167	138	1,217	161	84		29,565	156	3.43	1.49	2.30	0.17	9.5	4.1	1.13	.275	3.87	74	2.84	79	8.68	620
6	Tim Keefe T. Keefe	2.63	342	225	.603	600	594	2,564	554	39	2	5049.2	4,438	1,474	2,470	75	1,233	83	7		20,941	240	4.57	2.20	2.08	0.13	12.2	5.9	1.12	.257	4.40	79	2.92	87	7.91	239.2
7	Old Hoss Radbourn O. Hoss Radbourn	2.68	309	194	.614	527	502	1,830	488	35	3	4527.1	4,328	1,347	2,273	118	875	54	24		18,918	214	3.64	1.74	2.09	0.23	9.7	4.6	1.15	.262	4.52	82	3.15	95	8.60	51
8	Mickey Welch M. Welch	2.71	307	210	.594	565	549	1,850	525	41	4	4802.0	4,588	1,447	2,556	106	1,297	52	16		20,308	274	3.47	2.43	1.43	0.20	9.1	6.4	1.23	.264	4.79	88	3.28	103	8.60	-55.7
9	John Clarkson J. Clarkson	2.81	328	178	.648	531	518	1,978	485	37	5	4536.1	4,295	1,417	2,384	159	1,191	80	12		19,146	182	3.92	2.36	1.66	0.32	10.3	6.2	1.21	.263	4.73	75	3.35	88	8.52	289.8
10	Tom Seaver T. Seaver	2.86	311	205	.603	656	647	3,640	231	61	1	4783.0	3,971	1,521	1,674	380	1,390	76	6	116	19,369	126	6.85	2.62	2.62	0.72	18.8	7.2	1.12	.259	3.15	79	3.03	85	7.47	286.1
11	Pud Galvin P. Galvin	2.87	361	308	.540	697	681	1,799	639	57	1	5941.1	6,352	1,895	3,315	121	744	54	18		25,160	220	2.73	1.13	2.42	0.18	7.2	3.0	1.19	.278	5.02	94	2.97	95	9.62	94.5
12	Kid Nichols K. Nichols	2.96	361	208	.634	621	562	1,881	532	48	17	5067.1	4,929	1,664	2,480	156	1,272	129	56		21,082	169	3.34	2.26	1.48	0.28	8.9	6.0	1.22	.271	4.40	73	3.48	85	8.75	377.8
13	Lefty Grove L. Grove	3.06	300	141	.680	616	457	2,266	298	35	54	3940.2	3,849	1,339	1,594	162	1,187	42	123		16,622	51	5.18	2.71	1.91	0.37	13.6	7.1	1.28	.284	3.64	68	3.36	76	8.79	462.8
14	Warren Spahn W. Spahn	3.09	363	245	.597	750	665	2,583	382	63	28	5243.2	4,830	1,798	2,016	434	1,434	42	67	60	21,547	81	4.43	2.46	1.80	0.74	12.0	6.7	1.19	.258	3.46	84	3.44	94	8.29	124.4
15	Gaylord Perry G. Perry	3.11	314	265	.542	777	690	3,534	303	53	10	5350.0	4,938	1,846	2,128	399	1,379	108	33	164	21,953	160	5.95	2.32	2.56	0.67	16.1	6.3	1.18	.275	3.58	85	3.06	85	8.31	312.9
16	Roger Clemens R. Clemens	3.12	354	184	.658	709	707	4,672	118	46	0	4916.2	4,185	1,707	1,885	363	1,580	159	0	63	20,240	143	8.55	2.89	2.96	0.66	23.1	7.8	1.17	.284	3.45	70	3.08	71	7.66	680.4
17	Greg Maddux G. Maddux	3.16	355	227	.610	744	740	3,371	109	35	0	5008.1	4,726	1,756	1,981	353	999	137	3	177	20,421	70	6.06	1.80	3.37	0.63	16.5	4.9	1.14	.281	3.56	76	3.25	78	8.49	519.5
18	Nolan Ryan N. Ryan	3.19	324	292	.526	807	773	5,714	222	61	3	5386.0	3,923	1,911	2,178	321	2,795	158	13	78	22,575	277	9.55	4.67	2.04	0.54	25.3	12.4	1.25	.265	3.64	90	2.96	83	6.56	370.2
19	Steve Carlton S. Carlton	3.22	329	244	.574	741	709	4,136	254	55	2	5217.2	4,672	1,864	2,130	414	1,833	53	13	150	21,683	183	7.13	3.16	2.26	0.71	19.1	8.5	1.25	.279	3.67	87	3.14	86	8.06	271.5
20	Don Sutton D. Sutton	3.26	324	256	.559	774	756	3,574	178	58	5	5282.1	4,692	1,914	2,104	472	1,343	82	12	102	21,631	112	6.09	2.29	2.66	0.80	16.5	6.2	1.14	.261	3.58	92	3.23	90	7.99	181.2
21	Randy Johnson R. Johnson	3.29	303	166	.646	618	603	4,875	100	37	2	4135.1	3,346	1,513	1,703	411	1,497	190	7	37	17,067	109	10.61	3.26	3.26	0.89	28.6	8.8	1.17	.291	3.71	75	3.18	73	7.28	554.3
22	Phil Niekro P. Niekro	3.35	318	274	.537	864	716	3,342	245	45	29	5404.0	5,044	2,012	2,337	482	1,809	123	83	86	22,677	226	5.57	3.01	1.85	0.80	14.7	8.0	1.27	.270	3.89	87	3.61	95	8.40	116.1
23	Tom Glavine T. Glavine	3.54	305	203	.600	682	682	2,607	56	25	0	4413.1	4,298	1,734	1,900	356	1,500	66	0	145	18,604	65	5.32	3.06	1.74	0.73	14.0	8.1	1.31	.280	3.87	86	3.94	94	8.76	120.1
24	Early Wynn E. Wynn	3.54	300	244	.551	691	611	2,334	289	49	16	4564.0	4,291	1,796	2,037	338	1,775	64	67	36	19,408	51	4.60	3.50	1.31	0.67	12.0	9.1	1.33	.265	4.02	94	3.64	97	8.46	56.4