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Working at Height Fall Clearance Calculator

Required Fall Clearance (RFC) is the total vertical distance the worker's feet travel during an arrested fall, plus a safety buffer.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the lanyard length and, if the anchor sits below your harness D-ring, the extra free fall before the energy absorber engages.
  2. Enter (or accept the typical defaults for) the energy absorber deployment, harness stretch/D-ring shift, D-ring-to-feet height and safety margin.
  3. Optionally enter the available clearance from the anchor to the level below to see whether the setup is adequate or falls short.

How it works

Required Fall Clearance (RFC) is the total vertical distance the worker's feet travel during an arrested fall, plus a safety buffer. This calculator uses RFC = total free fall + deceleration distance + D-ring shift + worker height below the D-ring + safety margin, where total free fall = lanyard length + any extra free fall caused by the anchor sitting below the D-ring. It is measured straight down from the anchor point to the nearest obstruction.

The default figures (1.75 m absorber deployment, 0.3 m D-ring shift, 1.5 m worker height, 1 m margin) reflect commonly cited values in standards such as ANSI/ASSP Z359 and AS/NZS 1891, but every energy absorber, harness and anchor differs. Always substitute the exact values from the equipment manufacturer's data sheet and have a competent person verify the system before use.

Worked example

Shock-absorbing lanyard from an overhead anchor. A worker uses a 1.8 m shock-absorbing lanyard clipped to an anchor at D-ring height (0 m extra free fall). Using typical values — 1.75 m energy absorber deployment, 0.3 m harness stretch/D-ring shift, 1.5 m from D-ring to feet, and a 1 m safety margin — the required fall clearance is 1.8 + 0 + 1.75 + 0.3 + 1.5 + 1 = 6.35 m below the anchor. If only 6 m of clearance exists to the level below, the result flags a 0.35 m shortfall — NOT ENOUGH — so the worker must move to a higher anchor, a shorter lanyard, or a self-retracting device.

Common mistakes

  • Forgetting the worker's own height below the D-ring — the feet are what strike the ground, so the ~1.5 m from D-ring to feet must be included.
  • Assuming the anchor is overhead when it is at foot level. An anchor below the D-ring adds significant free fall (up to twice the lanyard length) and dramatically increases required clearance.
  • Using a shock-absorbing lanyard where clearance is tight. If the required clearance exceeds what is available, switch to a self-retracting lifeline (SRL) with a much shorter arrest distance, or raise the anchor.

Frequently asked questions

Is this fall clearance figure compliant with regulations?

This tool is guidance only. Required fall clearance depends on your exact equipment and jurisdiction. Follow your local WHS/OSH regulations, the equipment manufacturer's instructions, and standards such as ANSI/ASSP Z359 or AS/NZS 1891, and have a competent person or qualified professional verify any fall-arrest system before use.

Why is the deceleration distance 1.75 m by default?

1.75 m is a commonly cited maximum deployment distance for a shock-absorbing (energy-absorbing) lanyard. Your actual absorber may deploy more or less — always use the figure from the manufacturer's data sheet for the specific device and worker weight.

What if my anchor point is below my harness D-ring?

Then the worker free-falls further before the lanyard becomes taut, so enter that extra drop in the 'Extra free fall' field. A foot-level anchor can roughly double the free fall compared with an overhead anchor and greatly increases the clearance you need.

Does this account for a swing fall?

No. This calculation assumes a vertical fall directly below the anchor. A swing (pendulum) fall from an off-to-the-side position adds horizontal travel and the risk of striking obstructions — assess it separately with a competent person.

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