Baseball ISO Calculator

What is the ISO Calculator?

ISO (Isolated Power) is a sabermetric statistic that measures a batter’s raw power by calculating the difference between slugging percentage (SLG) and batting average (BA). This metric isolates pure power ability by excluding a batter’s capacity to get hits, focusing solely on their ability to hit for extra bases.

This calculator automatically computes your ISO value and provides FanGraphs-standard ratings by simply entering at-bats, hits, doubles, triples, and home runs data.

Calculation Method

Basic Formula

ISO = Slugging Percentage (SLG) – Batting Average (BA)

Or alternatively:

ISO = (Total Bases / At Bats) – (Hits / At Bats)

Detailed Calculation Steps

1. Singles (1B) = Hits – Doubles – Triples – Home Runs
2. Total Bases (TB) = Singles + (Doubles × 2) + (Triples × 3) + (Home Runs × 4)
3. Batting Average (BA) = Hits / At Bats
4. Slugging Percentage (SLG) = Total Bases / At Bats
5. ISO = Slugging Percentage – Batting Average

Rating Standards

ISO ratings based on FanGraphs official criteria:

• Awful: Below 0.080
• Poor: 0.080 – 0.100
• Below Average: 0.100 – 0.120
• Average: 0.120 – 0.140
• Above Average: 0.140 – 0.170
• Great: 0.170 – 0.200
• Excellent: 0.200 – 0.250
• Elite: Above 0.250

How to Use

1. Data Input

• At Bats (AB): Enter the officially recorded number of at-bats.
• Hits (H): Enter the total number of hits (includes singles, doubles, triples, and home runs).
• Doubles (2B): Enter the number of doubles.
• Triples (3B): Enter the number of triples.
• Home Runs (HR): Enter the number of home runs.

2. Calculate

After entering all data, click the “Calculate” button to display:

• Singles (1B) – automatically calculated
• Total Bases (TB)
• Batting Average (BA)
• Slugging Percentage (SLG)
• Isolated Power (ISO)
• ISO Rating

3. Sample Data

Three types of sample data are provided:

• Contact Hitter: High average, lower power (ISO ~0.120)
• Balanced Hitter: Balance of average and power (ISO ~0.200)
• Power Hitter: Power-focused approach (ISO ~0.300)

Key Features

Input Validation

The calculator automatically validates:

• At-bats must be at least 1.
• Hits cannot exceed at-bats.
• Combined extra-base hits cannot exceed total hits.
• All values must be 0 or greater.
• Singles calculation cannot result in negative values.

Dark Mode Support

Toggle between light and dark modes using the button in the upper right corner. The calculator automatically detects your system theme preferences, and manual changes are saved in your browser.

Responsive Design

Optimized display across all devices including desktop, tablet, and mobile.

Understanding ISO Values

What High ISO Means

A high ISO indicates excellent ability to hit for extra bases. An ISO above 0.200 represents elite power in professional baseball.

What Low ISO Means

A low ISO suggests a singles-focused approach. However, this isn’t necessarily negative – contact hitters with high batting averages and on-base percentages provide significant value to their teams.

ISO and Other Statistics

Since ISO is calculated as SLG minus BA:

• Batters with similar averages can have dramatically different ISO values based on extra-base hit production.
• A player with a lower batting average but many home runs may still post a high ISO.
• When combined with OPS (On-base Plus Slugging), ISO provides comprehensive insight into a player’s offensive contribution.

Practical Applications

Player Comparison

Compare ISO values to quickly determine which player possesses superior power. This metric effectively distinguishes power differences among players with similar batting averages.

Season Analysis

Track a player’s ISO across multiple seasons to identify trends in power development or decline. This helps evaluate whether a player’s power is improving, declining, or remaining stable over time.

League Context

The MLB league-average ISO is approximately 0.145. Use this benchmark to evaluate how a specific player’s power compares to league norms.

Version History

Release Notes

• March 27, 2025 – Initial Release v1.0
  • Basic ISO calculation functionality
  • 5-tier rating system
  • Sample data feature
• November 13, 2025 – Major Update v2.0
  • Fixed slugging percentage calculation error (improved singles calculation method)
  • Implemented FanGraphs official standards (expanded from 5 to 8 detailed rating tiers)
  • Added automatic singles (1B) calculation and display
  • Added total bases (TB) display feature
  • Complete dark mode support (automatic system detection + manual toggle)
  • Applied neobrutalism design system
  • Enhanced input validation system
  • Significantly improved responsive layout
  • Comprehensive user experience (UX) improvements

v2.0 Major Improvements

1. Enhanced Calculation Accuracy

Version 1.0 contained an error in slugging percentage calculation that improperly handled singles. Version 2.0 completely resolves this issue, providing accurate ISO values.

2. More Detailed Rating System

By implementing FanGraphs official standards, the rating system expanded from 5 to 8 tiers, enabling more precise power assessment.

3. Additional Information Display

Displaying singles and total bases makes the calculation process transparent and provides deeper insight into hitting patterns.

4. Dark Mode Implementation

Automatically detects and applies system theme preferences while allowing manual override. Reduces eye strain during nighttime use.

5. Modern Design

Implements neobrutalism design trends for a visually refined and intuitive interface.

Frequently Asked Questions

Q1. What’s the difference between ISO and slugging percentage?

Slugging percentage measures overall offensive production ability, while ISO specifically isolates power. By subtracting batting average from slugging percentage, ISO separates the ability to get hits from the ability to hit for power.

Q2. Can ISO be negative?

Theoretically, no. Since slugging percentage is always greater than or equal to batting average, ISO will always be zero or positive. A negative result indicates an input error.

Q3. Who has the highest ISO ever recorded?

The highest single-season ISO in MLB history belongs to Barry Bonds with 0.536 in 2001. Recent players like Aaron Judge and Giancarlo Stanton have also posted exceptionally high ISO values.

Q4. Does a high ISO always mean a good hitter?

Not necessarily. A player with high ISO but low batting average and high strikeout rate may not provide optimal offensive value. ISO should be evaluated alongside other metrics like OPS and wOBA for comprehensive assessment.

Q5. Why does the calculator show an error when extra-base hits exceed total hits?

The hits total includes singles, doubles, triples, and home runs. Therefore, the sum of doubles, triples, and home runs cannot exceed total hits. Please verify your hits input.

Reference Materials

• FanGraphs – ISO rating standards and sabermetrics resources
• Baseball Reference – Historical player statistics database
• MLB.com – Official baseball statistics and records

Contact and Feedback

For questions or suggestions regarding the ISO Calculator, please feel free to reach out. Your feedback helps us create better tools for the baseball community.