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ERA, WHIP & K/9 Calculator

Compute a pitcher's ERA, WHIP, K/9, BB/9, H/9, HR/9 and K/BB from innings pitched (in baseball thirds notation) and counting totals.

Enter innings pitched in thirds notation (e.g. 180.2 = 180 innings, 2 outs).

About this tool

The ERA, WHIP & K/9 Calculator turns a pitcher's box-score totals into the standard rate statistics. Enter innings pitched in baseball's thirds notation — where 180.1 means 180 innings and 1 out, and 180.2 means 180 innings and 2 outs — along with earned runs, hits, walks, strikeouts and home runs allowed. The tool converts the innings correctly before computing every rate.

Innings pitched are not a normal decimal: the fraction after the dot is a count of outs (0, 1, or 2), so IP is converted as outs = whole·3 + fraction, then IP = outs/3. From there ERA = 9·ER/IP, WHIP = (BB + H)/IP, and the per-nine rates K/9 = 9·K/IP, BB/9, H/9 and HR/9 follow, plus the strikeout-to-walk ratio K/BB. ERA estimates earned runs allowed per nine innings; WHIP measures base runners allowed per inning.

All calculations run locally in your browser, so your data never leaves the page. Entering an IP fraction greater than .2 is flagged as invalid because only .0, .1 and .2 are legal thirds. When a pitcher has zero walks the K/BB ratio is shown as infinite (∞) rather than a broken value, and the converted decimal innings are displayed so you can confirm the thirds were read correctly.

Frequently asked questions

What does 6.2 innings pitched mean?
It means 6 innings and 2 outs, not 6.2 in decimal. The digit after the dot counts outs (0, 1, or 2), so 6.2 IP equals 6 + 2/3 = 6.667 innings. The calculator converts this before computing ERA and the other rates.
How is ERA calculated?
ERA = 9 × earned runs / innings pitched, scaling earned runs to a full nine-inning game. A pitcher with 70 earned runs in 180.2 innings has an ERA of 9 × 70 / 180.667 ≈ 3.49. Only earned runs count, not runs from errors.
What is WHIP?
WHIP = (walks + hits) / innings pitched, the average number of base runners a pitcher allows per inning via walk or hit. A WHIP near 1.00 is excellent; it ignores how those runners score, unlike ERA.
Why is K/BB sometimes shown as infinity?
K/BB divides strikeouts by walks. With zero walks the ratio is mathematically infinite, so the tool shows ∞ instead of an error or a misleading number. Any positive walk total gives a normal ratio.

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