The Severity Rate is a critical Environmental, Health, and Safety (EHS) metric used to quantify the seriousness of workplace injuries and illnesses. While the Total Recordable Incident Rate (TRIR) measures the frequency of incidents, the Severity Rate measures the impact by calculating the number of lost workdays per 100 full-time equivalent employees.
A high severity rate indicates that workplace incidents are resulting in significant time away from work, signaling potential serious hazards that need immediate attention. Use the calculator below to determine your organization's Severity Rate based on the standard OSHA formula.
Calculate Your Severity Rate
Include days away from work and days of restricted work activity or job transfer.
The cumulative number of actual hours worked by all employees during the selected period.
function calculateSeverityRate() {
// 1. Get input values
var lostDaysInput = document.getElementById("totalLostDays");
var hoursWorkedInput = document.getElementById("totalEmployeeHours");
var outputDiv = document.getElementById("severityOutput");
// 2. Parse values to numbers
var days = parseFloat(lostDaysInput.value);
var hours = parseFloat(hoursWorkedInput.value);
// Ensure output div is visible for results or errors
outputDiv.style.display = "block";
// 3. Validate inputs (Edge case handling)
if (isNaN(days) || days < 0) {
outputDiv.innerHTML = "Please enter a valid, non-negative number for Total Lost Work Days.";
return;
}
if (isNaN(hours) || hours <= 0) {
outputDiv.innerHTML = "Please enter a valid total for Employee Hours Worked (must be greater than zero).";
return;
}
// 4. The Calculation Logic (OSHA Standard Formula)
// Formula: (Total Lost Days * 200,000) / Total Employee Hours Worked
// The 200,000 constant represents 100 employees working 40 hours/week for 50 weeks.
var severityRate = (days * 200000) / hours;
// 5. Format and Display Result
// Rounding to two decimal places for standard reporting
outputDiv.innerHTML = "Result: " + severityRate.toFixed(2) + " Severity Rate";
}
Understanding the Severity Rate Formula
The standard formula used by OSHA and many international safety organizations is:
Severity Rate = (Total Lost Work Days x 200,000) / Total Employee Hours Worked
Total Lost Work Days: This is the sum of days employees spent away from work or on restricted duty due to work-related injuries or illnesses during a specific time period (usually a year).
200,000 Constant: This figure normalizes the data to represent rate per 100 full-time employees (100 workers x 40 hours/week x 50 weeks/year). This allows for comparison between companies of different sizes.
Total Employee Hours Worked: The actual total number of hours worked by all employees during the same period covered by the lost days count.
Example Calculation
For example, if a manufacturing plant had 5 recordable incidents resulting in a total of 85 lost workdays over the course of a year, and their entire workforce logged a total of 450,000 hours worked: