A six foot lanyard does not need six feet
It needs about seventeen and a half. That is the whole reason this page exists, because the number written on the equipment is the number people plan around, and it is the first of five terms rather than the answer.
Six feet of lanyard, three and a half feet of deceleration as the shock absorber tears out, a foot of harness stretch as the webbing loads and the D-ring rides up, five feet from that D-ring down to your boots, and a couple of feet so you are not stopping level with the slab. Every one of those is real and four of them are invisible when you are standing on the steel looking at a lanyard.
Two questions that are not the same question
Is the free fall legal? 1926.502(d)(16)(iii) caps it at six feet, and that depends entirely on where the anchor sits relative to your D-ring.
Is there enough room? That is the sum above, and for a fixed lanyard it does not depend on the anchor height at all.
Merging those two is the common error, and it usually shows up as somebody raising an anchor and believing they have solved a clearance problem. Work it through: the slack is the lanyard length minus however far the anchor is above your D-ring, so the free fall is that difference. After the free fall your D-ring has travelled that difference, starting from a point that was already the anchor height below the anchor. Those two add back to exactly one lanyard length. The anchor height cancels.
So raising the anchor is worth doing and it buys a different thing: a shorter free fall, a legal one, and a lower arresting force on your body. It does not buy a single inch of room underneath.
Clipping low is the fatal version
Anchoring at foot level is easy. It is reachable without a second person, it needs no overhead steel, and a solid connection at your feet feels a great deal safer than nothing at all. With a six foot lanyard and a D-ring five feet above your boots it gives you eleven feet of free fall: the six of lanyard, plus the five you drop before the lanyard is even tight.
That is nearly double the legal maximum before any question of clearance, and the arresting force goes up with the distance, which is the other half of what the six foot limit is protecting. A system that stops you at 1,800 pounds from six feet is not stopping you at 1,800 pounds from eleven.
Which numbers you can argue with
Four of the figures here are law, from 1926.502(d): six feet of free fall, three and a half feet of deceleration, 1,800 pounds of arresting force with a body harness, and 5,000 pounds of anchorage per employee attached.
Two are not. Harness stretch is manufacturer data and varies by harness. The safety margin is industry practice, where ANSI Z359 works to two feet and plenty of manufacturers say three. Both are editable above, and the tool labels every line with where it came from, because somebody arguing a method statement needs to know which parts of seventeen and a half feet are negotiable.
The default margin here is two feet rather than three, which is the lower of the two commonly cited figures. A calculator that quietly pads its own answer is one nobody can check against their own equipment, and the padding always ends up hiding a real shortfall somewhere else.
When the room is not there
The usual answer is a self-retracting lifeline, and the reason is structural rather than a matter of quality: there is no lanyard length in the sum. An SRL pays out and locks within inches, so the clearance you need is the device's published arrest distance plus harness stretch, your height below the D-ring, and the margin. On the same defaults that is about eleven and a half feet against seventeen and a half.
The other answers are a shorter lanyard, which works and is often forgotten, or restraint rather than arrest: a lanyard short enough that you cannot reach the edge needs no clearance at all, because there is no fall to arrest.
Anchorage is per person, not per anchor
5,000 pounds is the figure everybody knows and the words after it are the ones that get dropped: per employee attached. Two people clipped to the same eyebolt need 10,000 pounds. It happens on every job where an anchor is convenient and a second man arrives, and the rating stamped on the anchor is almost never the one that situation needs.
The label on your harness outranks anything here
It adds up distances. It does not know your harness, your lanyard or your anchor, and the label on each of those outranks anything here. It assumes a vertical fall from a fixed anchor, so it does not cover a swing fall, where working off to one side of the anchor means you travel sideways as well as down and can strike something the clearance figure never considered. It does not cover horizontal lifelines, which sag under load and add to every figure above. And it does not cover a rescue plan, which is a separate obligation and the thing that decides what happens in the twenty minutes after the system works.
Common questions
How much fall clearance do I need for a 6 foot lanyard?
About 17 feet 6 inches below the anchor, on the usual planning figures: 6 feet of lanyard, 3.5 feet of deceleration, a foot of harness stretch, 5 feet from your dorsal D-ring down to your boots, and 2 feet of safety margin. The number people expect is six feet, because that is the length written on the lanyard. The eleven and a half feet of difference is where somebody hits the slab wearing equipment that worked exactly as designed.
Does raising the anchor give me more clearance?
No. For a fixed-length lanyard the anchor height cancels out of the sum, which is the part that surprises people. The slack is the lanyard length less however far the anchor sits above your D-ring, so after the free fall your D-ring is exactly one lanyard length below the anchor, wherever the anchor was. Raising it shortens the FREE FALL, which is a compliance question and a force question, and both of those matter. It does not make the room underneath any bigger. The only things that reduce required clearance are a shorter lanyard, a self-retracting lifeline, or working somewhere else.
What happens if I clip to something at foot level?
Your free fall roughly doubles. With a 6 foot lanyard and a D-ring 5 feet above your boots, anchoring at foot level gives 11 feet of free fall: the 6 feet of lanyard plus the 5 feet you drop before the lanyard is even taut. That is well over the 6 foot maximum in 1926.502(d)(16)(iii), and the arresting force rises with the distance. It happens because clipping low is easy and reachable and feels secure, which is exactly the problem.
What does OSHA actually require?
From 1926.502(d): the system must be rigged so an employee can neither free fall more than 6 feet nor contact any lower level; deceleration distance is limited to 3.5 feet; the maximum arresting force on the body with a body harness is 1,800 pounds; and the anchorage must support at least 5,000 pounds per employee attached. Those four are law. Harness stretch and the safety margin are not, and this tool says which is which on every line.
Is a legal free fall the same as enough clearance?
No, and the standard asks for both in one sentence. It says the system must be rigged so an employee can "neither free fall more than 6 feet, nor contact any lower level". Those are independent requirements. A perfectly compliant 6 foot free fall still kills you if the slab is fifteen feet down, because the free fall is only the first of five terms in the clearance sum. Passing the free fall limit is not the same as having room to stop.
Why does a self-retracting lifeline need less room?
Because there is no lanyard length in the sum. An SRL pays out and locks within inches, so the free fall is short whatever height you are working at, and the clearance you need is the device’s published arrest distance plus harness stretch, your height below the D-ring, and the margin. On the same defaults that is about 11 feet 6 inches against 17 feet 6 inches for a 6 foot lanyard. Six feet less room needed is usually the answer when somebody says there is not enough space here.
Two of us are clipped to the same anchor. Is that fine?
Only if the anchor is rated for both. 1926.502(d)(15) requires at least 5,000 pounds per employee attached, so two people on one point needs 10,000 pounds and not 5,000. Two men on the same eyebolt is the commonest version of this, and the figure on the eyebolt is almost never the one you need.
Where do the harness stretch and margin numbers come from?
Not from OSHA. Harness stretch is manufacturer data, because webbing elongates and the dorsal D-ring rides up under arrest, and a foot is the common planning allowance. The safety margin is industry practice: ANSI Z359 works to a minimum of two feet below the boots and plenty of manufacturers say three. Both are editable in the tool, and the default margin is the lower of the two commonly cited figures because a calculator that quietly pads its answer is one nobody can check.