Total hours worked by all employees during the period.
OSHA Standard (200,000 hrs)
International Standard (1,000,000 hrs)
200,000 represents 100 employees working 40 hours for 50 weeks.
Calculated Severity Rate
0.00
Understanding the Severity Rate Calculation Formula
The Severity Rate (SR) is a critical Key Performance Indicator (KPI) used in Environmental, Health, and Safety (EHS) management. While the Frequency Rate measures how often accidents happen, the Severity Rate measures the seriousness of those accidents by calculating the amount of time lost relative to the amount of time worked.
This metric helps organizations understand the impact of workplace injuries on productivity and employee well-being. A high severity rate often indicates that while accidents may or may not be frequent, the incidents that do occur result in significant time off work.
The Severity Rate Formula
The standard formula used by OSHA (Occupational Safety and Health Administration) and many other safety organizations is:
Severity Rate = (Total Lost Work Days × 200,000) / Total Employee Hours Worked
Component Breakdown:
Total Lost Work Days: The sum of all days employees could not work due to occupational injury or illness. This includes weekends if the medical recommendation requires rest, depending on specific reporting standards.
Total Employee Hours Worked: The aggregate number of hours worked by all employees during the reporting period (usually a year).
200,000: This is the standard base constant. It represents the equivalent of 100 full-time employees working 40 hours a week for 50 weeks a year (100 × 40 × 50 = 200,000).
Calculation Example
Let's assume a manufacturing plant has the following data for the year:
Total Hours Worked: 500,000 hours
Total Lost Days: 45 days due to injuries
Using the calculator above or the formula manually:
SR = (45 × 200,000) / 500,000
SR = 9,000,000 / 500,000
Severity Rate = 18
This means that for every 200,000 hours worked, 18 days were lost to injury.
Why Use 1,000,000 Hours Base?
While OSHA uses the 200,000 benchmark, some international standards and specific industries (like mining or large-scale construction) prefer a base of 1,000,000 hours to represent 500 full-time employees. Our calculator provides a dropdown option to toggle between these two standards depending on your reporting requirements.
Severity Rate vs. Frequency Rate
It is important not to confuse Severity Rate with Lost Time Injury Frequency Rate (LTIFR).
Frequency Rate: Counts the number of accidents. (Formula involves Number of Injuries).
Severity Rate: Counts the time lost due to accidents. (Formula involves Days Lost).
A company might have a high Frequency Rate but a low Severity Rate (many minor cuts requiring bandages). Conversely, a low Frequency Rate but high Severity Rate implies rare but catastrophic accidents (e.g., one major fall resulting in months of recovery).
Tips for Lowering Severity Rates
Risk Assessment: Identify high-risk tasks that cause severe injuries rather than just frequent minor ones.
Return-to-Work Programs: Implement modified duty programs to allow injured employees to return to lighter work sooner, reducing the "Lost Days" count safely.
Engineering Controls: Use physical barriers and guards to prevent contact with heavy machinery.
Training: Focus training on the specific hazards that lead to long-term incapacitation.
function calculateSeverity() {
// Get input values
var daysInput = document.getElementById('lostDays');
var hoursInput = document.getElementById('totalHours');
var baseInput = document.getElementById('baseConstant');
var resultContainer = document.getElementById('result-container');
var resultDisplay = document.getElementById('severity-result');
var errorMsg = document.getElementById('error-msg');
var interpretation = document.getElementById('interpretation-text');
// Parse values
var days = parseFloat(daysInput.value);
var hours = parseFloat(hoursInput.value);
var base = parseFloat(baseInput.value);
// Reset error state
errorMsg.style.display = 'none';
errorMsg.innerHTML = ";
resultContainer.style.display = 'none';
// Validation logic
if (isNaN(days) || days < 0) {
errorMsg.innerHTML = "Please enter a valid number for Lost Work Days (cannot be negative).";
errorMsg.style.display = 'block';
return;
}
if (isNaN(hours) || hours <= 0) {
errorMsg.innerHTML = "Please enter a valid number for Total Hours Worked (must be greater than 0).";
errorMsg.style.display = 'block';
return;
}
// Calculation Formula: (Lost Days * Base) / Total Hours
var severityRate = (days * base) / hours;
// Formatting result
// If result is an integer, show no decimals, otherwise show 2 decimals
var formattedResult = Number.isInteger(severityRate) ? severityRate : severityRate.toFixed(2);
// Display results
resultDisplay.innerHTML = formattedResult;
// Dynamic interpretation text based on the calculation
var baseText = (base === 200000) ? "100 full-time employees" : "500 full-time employees";
interpretation.innerHTML = "Result Interpretation: For every " + baseText + " (or " + base.toLocaleString() + " hours worked), approximately " + formattedResult + " days were lost due to injury.";
resultContainer.style.display = 'block';
}