You're scoring a game. The starter gets two outs in the 7th inning, then gets pulled. The reliever comes in and gives up a three-run homer. Who gets charged? How do you record the innings pitched? What about the ERA?
These mid-inning situations confuse even experienced scorekeepers. But once you understand the rules, calculating ERA for partial innings becomes straightforward.
This guide covers everything: how to record partial innings, who gets charged when inherited runners score, and how to handle every tricky ERA scenario you'll encounter.
Understanding Baseball's Innings Format
Before we tackle partial innings, you need to understand how baseball records innings pitched.
The Baseball Decimal System
Baseball doesn't use normal decimals. The number after the decimal point represents outs, not tenths.
| What You See | What It Means | Actual Decimal |
|---|---|---|
| 6.0 IP | 6 full innings (18 outs) | 6.000 |
| 6.1 IP | 6 innings + 1 out (19 outs) | 6.333 |
| 6.2 IP | 6 innings + 2 outs (20 outs) | 6.667 |
| 7.0 IP | 7 full innings (21 outs) | 7.000 |
The key point: .1 does not equal 0.1. It equals 1/3 (0.333...).
Why This System Exists
Baseball uses this format because an inning equals three outs. Recording partial innings as thirds makes logical sense:
- 1 out = 1/3 of an inning = .1
- 2 outs = 2/3 of an inning = .2
- 3 outs = 3/3 of an inning = 1.0 (full inning)
You'll never see .3, .4, .5, .6, .7, .8, or .9 in innings pitched. Those don't exist in baseball scoring.
The Most Common Mistake
People treat 6.1 IP as "six point one" (6.1) when calculating ERA. This is wrong. You must convert it to 6.333 first. Using 6.1 instead of 6.333 gives you an incorrect ERA — and this is the single most common error in ERA calculation.
Converting Innings Pitched for ERA Calculation
Here's exactly how to convert any innings pitched notation to the decimal you need for ERA calculations:
The Conversion Formula
IP (decimal) = Whole Innings + (Outs ÷ 3)
Step-by-Step Conversion
Example: Convert 45.2 IP
Step 1: Identify whole innings = 45
Step 2: Identify outs = 2
Step 3: Divide outs by 3 = 2 ÷ 3 = 0.667
Step 4: Add together = 45 + 0.667 = 45.667 innings
Result: Use 45.667 in your ERA calculation
Quick Reference Table
| Recorded As | Convert To | Calculation |
|---|---|---|
| X.0 IP | X.000 | X + (0 ÷ 3) |
| X.1 IP | X.333 | X + (1 ÷ 3) |
| X.2 IP | X.667 | X + (2 ÷ 3) |
Calculating ERA with Partial Innings
Now let's apply this to actual ERA calculations.
Example 1: Simple Partial Inning
Scenario
A pitcher allows 12 earned runs over 67.1 innings pitched.
Solution
Step 1: Convert 67.1 IP
67.1 = 67 + (1 ÷ 3) = 67.333 innings
Step 2: Apply ERA formula
ERA = (12 × 9) ÷ 67.333
ERA = 108 ÷ 67.333
ERA = 1.60
Answer: 1.60 ERA (elite performance)
Example 2: Two Outs Recorded
Scenario
A pitcher allows 28 earned runs in 156.2 innings pitched.
Solution
Step 1: Convert 156.2 IP
156.2 = 156 + (2 ÷ 3) = 156.667 innings
Step 2: Apply ERA formula
ERA = (28 × 9) ÷ 156.667
ERA = 252 ÷ 156.667
ERA = 1.61
Answer: 1.61 ERA
Inherited Runners: The Complex Part
This is where ERA calculation gets tricky. When a reliever enters mid-inning with runners on base, those runners are "inherited."
The Core Rule
Inherited runners who score are charged to the pitcher who put them on base, not the pitcher who allowed them to score.
This rule creates some unfair situations.
Example 3: Classic Inherited Runner Scenario
Scenario
Pitcher A starts the 7th inning. He allows a single, a walk, and another single to load the bases. His manager pulls him.
Pitcher B enters with bases loaded, nobody out. The next batter hits a grand slam.
Who Gets Charged?
Pitcher A: 3 earned runs (the three runners he put on base)
Pitcher B: 1 earned run (the batter who hit the homer)
Pitcher A's IP: 0.0 (no outs recorded)
Pitcher B's IP: 0.1 (1 out from the home run)
ERA Impact
Pitcher A: His ERA skyrockets. He allowed 3 runs without recording an out. His ERA for that appearance is infinite (mathematically undefined).
Pitcher B: 1 ER in 0.1 IP (0.333 innings) = (1 × 9) ÷ 0.333 = 27.00 ERA for that appearance
Why This Is Unfair
Pitcher A allowed three baserunners but didn't give up the hit that scored them. Pitcher B gave up the grand slam but only gets charged for one run. Both pitchers failed, but the ERA distribution doesn't reflect reality.
Example 4: Partial Inherited Runs
Scenario
Pitcher A: Allows a leadoff double in the 8th inning, then gets pulled after recording no outs.
Pitcher B: Enters with runner on 2nd, no outs. Allows a single (runner scores from 2nd), then gets the next three batters out.
Who Gets Charged?
Pitcher A: 1 earned run (his runner scored)
Pitcher B: 0 earned runs (the run that scored was inherited)
Pitcher A's IP: 0.0
Pitcher B's IP: 1.0 (three outs)
Result
Pitcher A gets hammered in ERA for one baserunner who scored while he was on the bench. Pitcher B gets a clean inning despite allowing the hit that scored the run.
Multiple Pitcher Scenarios
Things get even more complex when three or more pitchers work an inning.
Example 5: Three Pitchers, One Inning
Play-by-Play
Pitcher A starts the 9th:
- Allows a single (runner on 1st)
- Allows a walk (runners on 1st and 2nd)
- Gets pulled (0 outs recorded, 2 runners on base)
Pitcher B enters:
- Strikes out the first batter (1 out)
- Allows a single (runner from 2nd scores, runners on 1st and 3rd)
- Gets pulled (1 out recorded, 2 runners on base: 1 inherited from A, 1 he put on)
Pitcher C enters:
- Allows a double (both runners score)
- Gets final two outs
Final Tally
Pitcher A:
- 2 earned runs (both his runners scored)
- 0.0 IP
- Infinite ERA for the inning
Pitcher B:
- 1 earned run (the runner he put on 1st scored)
- 0.1 IP
- 27.00 ERA for the inning
Pitcher C:
- 0 earned runs (both runners were inherited)
- 0.2 IP
- 0.00 ERA for the inning despite giving up the hit that scored both runs
Special Cases and Edge Situations
What Happens When a Pitcher Records Zero Outs?
If a pitcher enters, allows baserunners, and gets pulled without recording an out, his IP for that appearance is 0.0.
This creates a mathematical problem: you can't divide by zero when calculating ERA.
Solution: The ERA for a single appearance with 0.0 IP is technically infinite (or undefined). Over a season, those 0.0 IP appearances are included in the pitcher's total IP, so the season ERA can still be calculated normally.
Example 6: Starter Leaves After 0.0 IP
Scenario
A starter loads the bases on three walks, then gets injured. He exits with 0.0 IP, 0 ER (no runs scored yet), 3 runners on base.
The reliever enters and allows a grand slam. All four runs score.
Scoring
Starter: 3 ER, 0.0 IP (his three runners scored)
Reliever: 1 ER, 0.1 IP (the batter)
Starter's season stats: If he had 45.1 IP and 15 ER before this game, he now has 45.1 IP and 18 ER. His ERA = (18 × 9) ÷ 45.333 = 3.57
Errors and Unearned Runs in Partial Innings
Errors complicate ERA calculations even further.
Example 7: Error Affects Multiple Pitchers
Situation
Two outs, bases empty in the 7th inning.
Pitcher A:
- Batter reaches on an error
- Next batter singles (runner to 3rd)
- Pitcher A gets pulled (2 outs, runners on 1st and 3rd)
Pitcher B enters:
- Allows a double (both runners score)
- Gets final out
Who Gets Charged?
Run #1 (the error runner): Unearned to both pitchers
Run #2 (the single): Earned run charged to Pitcher A
Pitcher A: 1 ER, 0.2 IP
Pitcher B: 0 ER, 0.1 IP (both runs were inherited)
Calculating Season ERA with Partial Innings
Here's how to calculate a pitcher's full-season ERA when they have multiple partial-inning appearances:
Example 8: Full Season Calculation
Pitcher's Season Stats
- Game 1: 6.1 IP, 2 ER
- Game 2: 5.2 IP, 1 ER
- Game 3: 7.0 IP, 0 ER
- Game 4: 4.1 IP, 3 ER
- Game 5: 6.2 IP, 2 ER
Step 1: Add Up Total Innings
6.1 + 5.2 + 7.0 + 4.1 + 6.2 = 29.6 IP (in baseball notation)
But you can't just add these decimals! You need to count outs:
- 6.1 = 19 outs
- 5.2 = 17 outs
- 7.0 = 21 outs
- 4.1 = 13 outs
- 6.2 = 20 outs
Total outs: 19 + 17 + 21 + 13 + 20 = 90 outs
Total innings: 90 ÷ 3 = 30.0 IP
Step 2: Add Up Earned Runs
2 + 1 + 0 + 3 + 2 = 8 ER
Step 3: Calculate ERA
ERA = (8 × 9) ÷ 30.0
ERA = 72 ÷ 30
ERA = 2.40
Pro Tip: Count Outs, Not Decimals
When adding up innings across multiple appearances, convert everything to outs first. Add the outs together, then divide by 3 to get total innings. This prevents the error of treating .1 and .2 as regular decimals.
Why Inherited Runners Make Relief ERA Misleading
The inherited runner rule creates a major flaw in ERA as a statistic for relievers.
The Problem
A reliever can:
- Enter with bases loaded, nobody out
- Give up a bases-clearing double
- Get three quick outs
- Finish with 0.00 ERA for that inning
Meanwhile, the starter who put those runners on gets crushed in ERA despite not giving up the big hit.
Better Stats for Relievers
Because of this flaw, analysts track additional stats for relievers:
- Inherited Runners Scored %: What percentage of inherited runners score?
- FIP (Fielding Independent Pitching): Removes defense and luck
- RE24: Measures run expectancy change
- Leverage Index: Measures game situation difficulty
These stats give a more complete picture than ERA alone.
Common Mistakes to Avoid
Mistake #1: Adding .1 and .1 to Get .2
Wrong: Pitcher throws 5.1 IP in one game and 4.1 IP in another = 9.2 IP total
Right: 5.1 = 16 outs, 4.1 = 13 outs, total = 29 outs = 9.2 IP
In this case, the wrong method happens to give the right answer. But try 5.2 IP + 4.2 IP:
Wrong: 5.2 + 4.2 = 9.4 IP
Right: 5.2 = 17 outs, 4.2 = 14 outs, total = 31 outs = 10.1 IP
See the problem? Never add IP decimals like normal decimals.
Mistake #2: Forgetting to Convert Before Calculating ERA
Wrong: 15 ER in 45.1 IP → ERA = (15 × 9) ÷ 45.1 = 2.99
Right: 15 ER in 45.1 IP (45.333) → ERA = (15 × 9) ÷ 45.333 = 2.98
The difference is small in this example, but it compounds over time.
Mistake #3: Charging the Wrong Pitcher for Inherited Runs
Rule to remember: Inherited runners are ALWAYS charged to the pitcher who put them on base, regardless of who allows them to score.
Practice Problems
Problem 1
A pitcher allows 18 earned runs over 72.2 innings. Calculate his ERA.
Click to see answer
Step 1: Convert 72.2 IP = 72.667
Step 2: ERA = (18 × 9) ÷ 72.667 = 2.23
Answer: 2.23 ERA
Problem 2
Pitcher A allows two singles and gets pulled (0 outs, 2 runners on). Pitcher B enters and allows a 3-run homer. Who gets charged with what?
Click to see answer
Pitcher A: 2 ER, 0.0 IP
Pitcher B: 1 ER, 0.1 IP
The two inherited runners score = 2 ER to Pitcher A
The batter who homered = 1 ER to Pitcher B
Problem 3
Add these innings together: 6.2 IP + 5.1 IP + 7.2 IP. What's the total?
Click to see answer
Count outs:
- 6.2 = 20 outs
- 5.1 = 16 outs
- 7.2 = 23 outs
Total: 59 outs = 19.2 IP
Answer: 19.2 IP
The Bottom Line
Calculating ERA with partial innings requires three key skills:
1. Convert innings properly: .1 = 0.333, .2 = 0.667, never add decimals directly
2. Track inherited runners: They're charged to the pitcher who put them on base
3. Count outs, not decimals: When adding innings across multiple appearances, count total outs then divide by 3
Master these three concepts and you'll handle any ERA calculation scenario — even the tricky mid-inning substitutions that confuse most scorekeepers.
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