How do I hang a tree swing safely, and which branch is strong enough?

The short answer

Pick a live hardwood branch at least 8 inches in diameter, drill straight through it, and hang the swing from a drop-forged eye bolt held by a washer and a locked nut. Then measure the ground: the swing needs clear space twice the branch height in front and behind.

No safety standard covers tree swings. The answer comes from three places: tree care guides for the branch, the arborist standard for hardware in trees, and the CPSC playground handbooks for the swing geometry.

Which branch is strong enough

Every guide cited here gives the same floor: a branch at least 8 inches in diameter⁶⁷⁸⁹. You may also see 8 to 12 inches. None of these sources gives 12 inches as the minimum, so treat 8 as the floor and the extra as margin.

Diameter is necessary, not sufficient. ISA Certified Arborists Eric Putnam and Shane Krajnik add that the branch should be a scaffold limb, "one that connects directly to the main trunk of the tree", joined in a U shape rather than a V, and free of cracks, included bark and decay⁷. The International Society of Arboriculture's own checklist names cracks or splits "where branches are attached" and codominant stems as likely failure points⁵.

Species lists overlap but do not agree:

Oak is on every list; willow and birch are on every avoid list. Where the lists disagree, as on pines, the branch's condition decides. Today's Homeowner caps the branch at 20 feet⁹, but the use zone below rules out a high branch long before that.

How far from the trunk

Tree guides say 3 feet (Davey) or 3 to 5 feet (Cottage Life, Today's Homeowner)⁶⁸⁹. That keeps the swing off the trunk. It is not the play safety number.

The CPSC home handbook asks for play equipment "at least 6 feet from any structure or obstacle", and names trees². The public handbook sets the side zone of a to-fro swing at 6 feet from the swing¹. A two-rope swing moves at right angles to the branch, so the trunk sits beside it. Hang it so the edge of the seat is at least 6 feet from the trunk, and on a branch that is still 8 inches thick at that point.

The space a tree swing needs

The CPSC public handbook sets the clear zone in front of and behind a belt swing at twice the vertical distance from the pivot to the surface below¹. The home handbook says the same: twice the height of the bar the swing hangs from². On a tree, the bar is the branch.

The corridor has to be free of the trunk, other trees, low branches, roots, fences and sheds; the home handbook lists low overhanging branches, stumps and roots as hazards to clear². Run your own numbers in the use zone calculator, and see fall height and use zones for how the measurement is taken.

Bolt it through: 1/2 inch or 5/8 inch

The guides split on bolt size. Today's Homeowner and Putnam and Krajnik use a 1/2 inch eye bolt⁹⁷; Cottage Life wants a 5/8 inch shouldered eye bolt or larger⁸. No standard settles it, because no standard sizes hardware for swings. What the arborist sources do settle is the type of hardware:

• Drop-forged. Texas A&M AgriLife: for tree support systems in the US, only drop-forged eye bolts "are accepted & approved"⁴. Putnam and Krajnik specify forged hardware rated at least 2,200 lb⁷.
• Through the limb. AgriLife calls lag screws "usually considered the weakest portion" of a system, warns they can pull out as the tree moves, and rules them out in decayed limbs⁴.
• Tight hole. ANSI A300 holds holes for through-hardware to no more than 1/8 inch over the hardware diameter³.
• Washer and secured nut. A300 requires heavy-duty round washers under the nut, not countersunk into the wood, with nuts secured against loosening³. Putnam and Krajnik double-nut⁷.

So buy the forged bolt with a stated rating, whichever size. A bent-wire eye fails that test even at 5/8 inch. Nuts on wood loosen, so hardware and fasteners applies here too.

Never wrap rope, chain or a strap around the limb. Putnam and Krajnik warn that wrapping girdles and abrades the branch, and slings compress the living tissue under the bark⁷. Davey's rubber sleeve reduces the rubbing, but Davey still says to replace the rope as the branch widens to avoid girdling⁶. The treehouse guide makes the same point for platforms: a few clean bolt wounds beat a wrap.

Rope or chain below the bolt

The CPSC public handbook says fiber ropes "are not recommended as a means of suspending swings since they may degrade over time"¹. Putnam and Krajnik hang from galvanized 3/8 inch Grade 30 proof chain with a forged swivel and 3/8 inch stainless quick links⁷. Chain is the choice both handbooks accept, and coated chain spares fingers, as the swings guide explains.

The home handbook does allow rope, but not rope "that can untwist or separate", because the gap can trap a child². Three-strand twisted rope can be pulled apart that way, so if you use rope, use braided rope and check it monthly. Davey's 3/4 inch minimum⁶ is a rope size, not a reason to skip the checks.

Avoid a single free-hanging rope with a knot or a loop. The public handbook advises against free-swinging ropes "that may fray or otherwise form a loop" because of the strangulation risk¹, and protrusion and entanglement explains how loops catch.

Seat height and what goes underneath

Davey sets the seat about 24 inches off the ground⁶. Cottage Life adds that under load it should sit at about half that⁸. The CPSC public handbook asks for at least 12 inches between a belt seat and the surfacing, measured after loose fill has compacted¹. Set 24 inches unloaded and check it with an adult sitting on it.

Davey suggests hanging the swing over grass⁶. The CPSC home handbook says grass and dirt "are not considered protective surfacing"², one of the mistakes in what not to use under play equipment, and recommends 9 inches of wood mulch, engineered wood fiber or rubber mulch for equipment up to 8 feet high. The public handbook makes the fall height of a swing the height of the pivot¹, so a 12 foot branch is past the home table and the depth has to come from the depth and fall height chart. Backyard surfacing compares the materials, and surfacing under swings covers the hollow that forms under the seat.

Inspecting the tree and the swing

A swing adds a cyclic load to a living limb, so the tree is part of the inspection.

The A300 inspection annex for hardware in trees adds the growth of the tree and the effect of the hardware on it³. If you answer yes to anything on the ISA checklist, the brochure says to have the tree examined by an ISA Certified Arborist⁵. Fold the rope and bolt check into your annual maintenance routine.

Where this stops applying

The CPSC handbooks were written for manufactured play equipment, and A300 for cabling and bracing, not for swings. Applying them to a tree is a conservative reading, not a rule anyone enforces. No figure here tells you what load a given branch will carry; an arborist judges that standing under it. Adult rope swings over water and hammocks are outside this page.

What to do next

Measure first. If twice the branch height does not fit your yard in both directions, no bolt fixes it, and a framed swing set with a lower beam is the better buy: check it with the playset fit checker, and see small yards and choosing a playset. If it fits, book an arborist to look at the branch before you drill, then use swing safety for the seat and hardware checks that apply to every swing.