Man-Hours / Exposure Hours Calculator

Calculates total hours worked across multiple employee/worker groups — the denominator figure needed for OSHA Form 300A and every incident-rate calculator (TRIR, LTIFR, DART, PSE rate).

OSHA convention: "Hours worked" includes time actually on the job for all employees — salaried, hourly, part-time, seasonal, and supervised temporary/contract workers. It excludes vacation, sick leave, holidays, and other paid time off, even though paid. For salaried employees whose hours aren't individually tracked, a common accepted estimate is 2,000 hours/year (40 hrs/week × 50 weeks), adjusted for known extended absences.

Employee / Worker Groups

Total Workers (all groups)

Avg Hours / Worker

Total Hours Worked

Formula Reference

Group Hours = Number of Workers × Average Hours per Week × Number of Weeks Worked
Total Hours Worked = Σ (Group Hours, across all groups)

Where This Number Is Used

TRIR	(Recordable Cases × 200,000) ÷ Total Hours Worked
LTIFR	(Lost Time Injuries × Base Hours) ÷ Total Hours Worked
DART Rate	(DART Cases × 200,000) ÷ Total Hours Worked
API RP 754 PSE Rate	(PSE Count × 200,000 or 1,000,000) ÷ Total Hours Worked
OSHA Form 300A	Reported directly as "Total hours worked by all employees"

Methodology, interpretation & sources

Purpose. Calculates total hours worked across multiple employee/worker groups — the denominator figure needed for OSHA Form 300A and every incident-rate calculator (TRIR, LTIFR, DART, PSE rate).

How to use the result. Start with source data you can verify, enter values on a consistent unit and time basis, and record the assumptions used. The main inputs on this page include the values requested on the form. Re-run the calculation when those assumptions change rather than carrying an old result forward.

Decision use. Use this calculator to standardize a safety-performance indicator from your own verified incident and exposure data. Consistent definitions are essential when comparing sites or time periods.

Limitations. Confirm that the numerator event definition and denominator exposure-hours basis match the reporting framework used by your organization or regulator.

Primary references. Use the current edition/version that applies to your jurisdiction and organization:

Editorial note. Prepared and maintained by Impact Tech Solutions. Editorially updated 28 September 2026. No individual professional credential is claimed on this page; high-consequence, statutory, tax, engineering or health decisions should be independently verified against the current primary source and, where required, a qualified professional.

Verification checklist before relying on this result

Confirm the source and date of the main input values and keep units consistent.
Check that zero, blank, percentage and currency entries mean what the calculator expects; do not use a placeholder value as real data.
Repeat the calculation with a plausible low and high assumption to see whether the decision changes materially.
Record the result together with the assumptions, not as a stand-alone number.
For statutory, tax, engineering, health or safety decisions, compare the output with the current primary requirement and obtain competent review where required.

A calculator is most useful when it makes assumptions visible. If a small input change produces a very different outcome, treat that sensitivity as part of the decision rather than selecting only the most favorable result.