Fall Protection Clearance Calculator
Calculate required fall clearance below an anchor point. ANSI Z359.13 formulas — verify with manufacturer specs.
Energy-absorbing lanyard length at full deployment.
Typical with a shock-absorbing lanyard. OSHA limits free fall to 6 ft max.
Max allowable elongation of energy absorber per ANSI Z359 (typically 3.5 ft).
Distance from harness D-ring down to the feet.
Recommended clearance margin (typically 3 ft).
Used to verify your harness/lanyard is rated for your weight.
Used to check whether you have enough fall distance for your system.
Required clearance below anchor
16.50 ft
Free fall + deceleration + worker height + safety factor
SETUP OK
Anchor at 20.00 ft provides 3.50 ft of margin above required clearance.
| Required clearance | 16.50 ft |
| Anchor height available | 20.00 ft |
| Clearance margin | 3.50 ft |
| Max arrest force (ANSI Z359 limit) | 1,800 lbs |
| Worker weight | 220 lbs |
| OSHA anchor minimum (1926.502(d)(15)) | 5,000 lbs |
| Engineered anchor min (2x MAF) | 3,600 lbs |
| Required anchor strength | 5,000 lbs |
OSHA + ANSI Z359 quick reference
- OSHA 1926.502(d)(15) — anchors must support 5,000 lbs per worker, OR be engineered with a safety factor of at least 2.
- OSHA 1926.502(d)(16) — personal fall arrest systems must limit max arrest force to 1,800 lbs when used with a body harness.
- Free fall must not exceed 6 ft, or contact with a lower level — whichever is less (1926.502(d)(16)(iii)).
- Deceleration distance must not exceed 3.5 ft (1926.502(d)(16)(iv)).
Methodology: Required clearance = free fall + deceleration + worker height (D-ring to feet) + safety factor. Anchor strength = max(OSHA 5,000 lbs per worker, 2 × max arrest force).
Frequently Asked Questions
What is "free fall distance" vs "fall arrest distance"?
Free fall distance is the vertical distance you fall before the fall arrest system starts to slow you down — typically from your D-ring to the point where the lanyard goes taut. OSHA caps this at 6 ft for a personal fall arrest system. Fall arrest distance is the total distance you travel from the start of the fall to coming to a complete stop — that includes free fall plus deceleration distance (the energy absorber stretching out). Required clearance below the anchor must accommodate both, plus your body length and a safety margin.
What anchor strength does OSHA require?
OSHA 1926.502(d)(15) requires anchorages used to attach personal fall arrest equipment to either (a) support at least 5,000 lbs per attached worker, or (b) be designed, installed, and used as part of a complete personal fall arrest system that maintains a safety factor of at least 2, under the supervision of a qualified person. Most jobsite anchors default to the 5,000 lb requirement because engineered systems require sign-off from a qualified person.
When should I use a self-retracting lifeline vs a lanyard?
Use a self-retracting lifeline (SRL) when you do not have enough fall clearance below the work surface for a 6 ft shock-absorbing lanyard. An SRL locks within inches of the start of a fall, drastically reducing free fall and total fall distance. SRLs are essential for low-clearance applications such as scissor lifts, low rooftops, and leading-edge work. Use a standard energy-absorbing lanyard when you have well over 16-18 ft of clearance below the anchor and want a simpler, cheaper system.
What if my required clearance is more than the height I'm working at?
You cannot use that system at that height. You will hit the lower level before the system fully arrests the fall — a fatal setup. Options: switch to a self-retracting lifeline that reduces free fall to inches, move the anchor higher (overhead anchor preferred), shorten the lanyard, use a fall restraint system that prevents reaching the edge in the first place, or install guardrails / safety nets as the primary fall protection instead. Always have a Competent Person verify your setup.
Estimates only. Not a substitute for OSHA-compliant fall protection plan, PE-stamped scaffolding design, or qualified-person ladder inspection. Verify with a Competent Person.