E Value Calculator

E Value Calculator can be used to estimate the probability of finding a match between two sequences by chance alone in database searches.

Input Parameters

Calculation Results

Calculation Formula

E-value = (Match Count × Sequence Length × 0.001) / Database Size

Where:
Match Count: Number of similar sequences found
Sequence Length: Length of query sequence in base pairs
Database Size: Total number of base pairs in database

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E Value Calculator Calculator Usage Guide

Learn how to use the E Value Calculator for sequence alignment analysis

What is E-value?

E-value (expect value) is a statistical measure used in bioinformatics to estimate the probability of finding a match between two sequences by chance alone in database searches. It's similar to p-value in hypothesis testing, where a lower E-value indicates a more significant match.

How to use this calculator:

  1. Enter the length of your query sequence in base pairs
  2. Enter the number of similar sequences found in the database
  3. Enter the sequence identity percentage (match rate)
  4. Enter the size of the database you're searching against (in base pairs)
  5. Click "Calculate" to compute the E-value

Interpreting Results:

The calculator will display the E-value and a assessment of its statistical significance. Generally:

  • E-value < 0.0001: Extremely significant match
  • E-value < 0.001: Very significant match
  • E-value < 0.01: Significant match
  • E-value < 0.05: Moderately significant match
  • E-value < 0.1: Weakly significant match
  • E-value ≥ 0.1: Not significant (could be by chance)

Practical Applications:

E-value is commonly used in BLAST (Basic Local Alignment Search Tool) searches to evaluate the significance of sequence alignments. When comparing results across different searches, you should consider both the E-value and the percent identity to make informed biological conclusions.