Fall Clearance Calculator (Lanyard, Anchor Height & Free Fall)
A shock-absorbing lanyard needs far more room below the anchorage than its own length. This calculator adds the lanyard, the deceleration distance, the height of the suspended worker and a safety factor, compares the total with the clearance you measured, and flags a free fall over the 6 ft limit of 29 CFR 1926.502(d)(16)(iii).
Required clearance below the anchorage
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Results are estimates for planning purposes and do not replace a competent person's evaluation or an engineer's design. Follow the OSHA standards that apply to your work and your employer's written program.
The four distances that stack up
Every one of them is below the anchorage at the moment the fall is arrested, which is why the required clearance is far more than the length of the lanyard.
| Symbol | Distance | Starting value | Where the number comes from |
|---|---|---|---|
| LL | Lanyard length | 6 ft | The connecting subsystem at its full length, energy absorber included, before it deploys. Printed on the lanyard. |
| DD | Deceleration distance | 3.5 ft | How far the energy absorber lets the worker travel while it brings them to a stop. 3.5 ft (1.07 m) is the maximum OSHA allows — 1926.502(d)(16)(iv). Your label may say less. |
| HH | Height of the suspended worker | 6 ft | Back D-ring down to the boots of a worker hanging in the harness. |
| C | Safety factor | 1.5 ft | Covers D-ring slide and harness stretch, plus the error in your own measurement. 1.5 ft is the figure in 3M's clearance chart; a number of employer programs use 3 ft. |
The starting values are what the calculator loads. Replace them with the figures on your own equipment: the label on the energy absorber and the manufacturer's clearance chart govern, not a generic default.
Four common setups
All four assume a 6 ft suspended worker, a 3.5 ft deceleration distance and a 1.5 ft safety factor. Only the lanyard and the position of the anchorage change.
| Setup | Free fall | Clearance needed below the anchorage | What it means |
|---|---|---|---|
| 6 ft lanyard, anchorage level with the D-ring | 6.0 ft | 17.0 ft | Free fall is right at the 6 ft cap. Legal, but Appendix C (k) asks you to keep it shorter. |
| 6 ft lanyard, anchorage 2 ft above the D-ring | 4.0 ft | 17.0 ft | Same clearance needed, lower free fall and lower arresting force. This is what "anchor overhead" buys you. |
| 4 ft lanyard, anchorage 2 ft above the D-ring | 2.0 ft | 15.0 ft | Shortening the lanyard is the only change here that reduces the clearance you need. |
| 6 ft lanyard tied off at the walking surface, D-ring 5 ft above it | 11.0 ft | 17.0 ft | Free fall almost doubles the 6 ft limit of 1926.502(d)(16)(iii). Not an acceptable rigging, whatever the clearance. |
Read the last two rows together
Raising the anchorage cuts the free fall but not the clearance. Only a shorter connecting device — or one that keeps the line taut — reduces the room you need below you. That is the trade-off to bring to whoever selects the equipment.
Measuring the clearance you have
- Start at the anchorage connection point, not at your feet and not at the guardrail. Manufacturers' charts are drawn that way, and it is the one reference that does not move as you work.
- Stop at the first thing you could hit: the lower level, a slab edge, scaffold planks, a stack of material, a truck bed, a piece of equipment parked below. Not the ground, if something is in the way.
- Take the worst position you will occupy on that anchorage. Clearance is checked where it is smallest.
- Re-check when the job changes. Decking a floor, moving a lift or dropping a material pile underneath changes the answer without anyone touching the harness.
- Write it down in the pre-task plan or the JHA with the anchorage it belongs to, so the next crew is not re-deriving it from memory.
What this calculator does not cover
- Swing fall. The numbers are for a fall straight down. Anchored off to the side, a worker swings, travels further, and can strike whatever is beside them — Appendix C (m) tells you to pick tie-offs that minimize it.
- Self-retracting lifelines. An SRL's required clearance comes from its own label and depends on the mounting, the worker's weight and the arrest distance of that device. Do not use the lanyard arithmetic on one.
- Horizontal lifelines and long vertical lifelines. Both sag and stretch under load, and that adds to the fall. A horizontal lifeline has to be designed by a qualified person — 1926.502(d)(8).
- Anchorage strength. Clearance says the fall stops above the lower level; the anchorage says it stops at all. 1926.502(d)(15) requires at least 5,000 lb per employee attached, independent of any platform anchorage, or a system designed by a qualified person with a safety factor of at least two.
- Rescue. A worker hanging in a harness needs prompt rescue — 1926.502(d)(20). Suspension trauma starts long before a fire crew arrives.
- Whether fall arrest is the right choice at all. Guardrails, covers, nets or a travel restraint that keeps you from reaching the edge need no clearance below and no rescue plan.
How it's calculated
- Required clearance below the anchorage
RD = LL + DD + HH + CPure geometry once the fall is arrested: the worker hangs the lanyard length plus the deployed energy absorber below the anchorage, and their boots hang one body length further down. The safety factor absorbs D-ring slide and harness stretch.- Free fall distance
FFD = LL + (height of the D-ring above the anchorage)Zero offset when the anchorage is level with the D-ring, so FFD = LL. Tie off at the working surface and the free fall is the lanyard plus the height of the D-ring above that surface — the case Appendix C (k) works through. Tie off overhead and the free fall is shorter than the lanyard.- Total fall distance
TFD = FFD + DDAppendix C (l): the stretch of the lanyard and the stopping distance of the deceleration device are added to the free fall distance to get the distance travelled before the worker is fully stopped.- The check this tool performs
clearance available below the anchorage ≥ RD, and FFD ≤ 6 ft (1.8 m)Both must hold. 1926.502(d)(16)(iii) requires the system be rigged so the employee can neither free fall more than 6 ft nor contact any lower level. This tool verifies a clearance you measured — it does not design a fall arrest system.
Frequently asked questions
With the numbers this calculator starts from — a 6 ft lanyard, the 3.5 ft maximum deceleration distance of 1926.502(d)(16)(iv), a 6 ft suspended worker and a 1.5 ft safety factor — you need 17 ft below the anchorage. Change any of those and the answer changes, so use the deceleration distance printed on your own energy absorber and measure your own clearance.
From the anchorage connection point, straight down. That is how manufacturers' clearance charts are drawn, and it is the only reference that stays fixed while you move around. If you measure from the walking surface instead, you have to add or subtract the height of the anchorage above that surface — an easy way to lose several feet.
Because the free fall distance is the lanyard plus the distance your D-ring sits above the anchorage. Appendix C (k) spells it out: with a 6 ft lanyard tied off at the working level, the free fall is 6 ft plus the height of the attachment point on your back, so roughly 11 ft. That is over the 6 ft limit of 1926.502(d)(16)(iii), and the arresting force climbs with it.
Do not shorten the safety factor. Change the system: move the anchorage higher, use a shorter lanyard, switch to a self-retracting lifeline with a short arrest distance, or eliminate the exposure with guardrails, a net, or a restraint system that stops you reaching the edge. A qualified person makes that call — a fall arrest system that cannot arrest above the lower level is not fall protection.
Usually yes, because the line stays taut and the free fall is short, but the required clearance still comes from the label on that specific SRL and depends on how it is mounted, the worker's weight, and whether the anchorage is overhead or at foot level. Do not run an SRL through this calculator: use its own chart.
3.5 ft (1.07 m) is the maximum OSHA allows for the system — 1926.502(d)(16)(iv) and 1910.140(d). The actual figure is on your energy absorber's label and is often shorter. Some manufacturers publish a larger allowance in their clearance charts to stay conservative for heavier users or a free fall over 6 ft on equipment designed and tested for it; when the label and this default disagree, the label wins.
No. Appendix C (m) warns that a tie-off away from directly overhead lets a falling worker swing, and the swing both increases the distance travelled and puts them into whatever is beside them. Anchor as close to directly overhead as you can, and treat the clearance from this tool as valid only for a vertical fall.
They are separate duties and you need both. 1926.502(d)(15) requires an anchorage independent of any platform anchorage and capable of supporting at least 5,000 lb per employee attached, or a system designed by a qualified person with a safety factor of at least two. Clearance says the fall stops above the ground; the anchorage says it stops at all.
Sources & references
- 29 CFR 1926.502(d)(16) — Personal fall arrest systems: no free fall over 6 ft, no contact with a lower level, deceleration distance limited to 3.5 ft, arresting force limited to 1,800 lb with a body harness
- 29 CFR 1926 Subpart M, Appendix C — Personal Fall Arrest Systems (non-mandatory guidelines): (k) free fall distance and the working-level tie-off example, (l) elongation and deceleration added to reach total fall distance, (m) obstructions and swing fall
- 29 CFR 1910.140(d) — General industry personal fall arrest systems: same 3.5 ft deceleration limit; a free fall over 6 ft only where the employer can demonstrate the manufacturer designed and tested the system for it
- 3M Fall Protection — Fall Clearance Calculation Chart (9700606 REV B): RD = LL + DD + HH + C, measured below the anchorage connection point; D-ring slide and harness stretch built into C — Manufacturer document. Always use the chart printed on the equipment you actually own.
- 29 CFR 1926.501(b) — Where fall protection is required in construction (6 ft over a lower level for most work)
Content checked against these sources — last reviewed August 28, 2026.