This hammock hang calculator exists mainly to make one number visible. When you hang a hammock, the force on each anchor is not half your body weight. At a shallow angle it can be several times your entire body weight, and the shallower and tighter you pull the hang, the worse it gets. People routinely hang hammocks flat and tight because it looks tidy, without realising that they have multiplied a 200 pound load into most of half a ton at each tree.
The geometry — how high to attach, how long the suspension needs to be — is the part people usually come looking for, and it is here too. But Arb Digital built the page around the force, because that is the number that decides whether a strap, a carabiner, a screw eye or a branch is being asked to do something it was never rated for. A hammock failure drops an adult from sitting height onto their back or head, often with hardware following.
What This Calculator Does, and What It Refuses To Do
It computes four things from a level, symmetric hang: the static force on each anchor, the height at which the suspension meets each anchor, the suspension length needed per side, and how far the hammock body sags below its ridgeline. It also plots anchor force across a range of hang angles, which makes the point better than any paragraph.
It refuses three things deliberately. It publishes no strength figures for straps, rope, carabiners or trees, because those are properties of specific products and specific living organisms and a number recalled from memory into a load calculation is worse than no number. It declines to compute an uneven hang, for reasons set out below. And it never states that a setup is safe, adequate or strong enough — not in any wording, not anywhere.
How to Use It
- Confirm the anchors are at the same height. If they are not, this tool will not compute the hang, and the reason is explained further down.
- Measure the distance between the anchors and the gathered end-to-end length of the hammock itself, both in the same unit.
- Set the hang angle. Thirty degrees is the widely used starting point among hammock campers; the bars will show you what happens either side of it.
- Enter the total weight the hammock will carry, including the hammock, an underquilt and anything else hanging in it.
- Read the working load limit off your actual hardware and enter it, then look at the comparison rather than at a reassuring word, because there is not one.
The Geometry and the Force Relation
The force result is a straight application of static equilibrium, the conditions set out in the Physics LibreTexts treatment of conditions for static equilibrium. The total weight W hangs from two suspension lines, each making an angle θ with the horizontal. Vertical forces must sum to zero, so the vertical component of each line’s tension carries half the weight:
F = W ÷ (2 · sin θ)
That is the whole thing, and its behaviour is brutal. At 30 degrees, sin θ is 0.5, so F equals W exactly — each anchor takes the full body weight, not half of it. At 15 degrees the multiplier is 1.93. At 10 degrees it is 2.88. At 5 degrees it is 5.74. As the angle approaches zero the force approaches infinity, which is the mathematical statement of a fact every rigger knows: you cannot pull a loaded line perfectly straight.
The height calculation follows from the same geometry. The horizontal run of each suspension line is half the difference between anchor spacing and ridgeline length, and the line rises across that run by the run times the tangent of the angle. Below the ridgeline the hammock body sags; this tool models it as a circular arc of the hammock’s own length subtending the ridgeline as its chord, solved numerically. Anchor height is sit height plus rise plus sag.
Worked example with the defaults, which you can check by hand. A 200 pound occupant plus 5 pounds of gear is 205 pounds total. At 30 degrees, F = 205 ÷ (2 × 0.5) = 205 pounds on each anchor. At 10 degrees, F = 205 ÷ (2 × 0.17365) = 590.3 pounds. On the geometry: a 132 inch hammock at 83 per cent gives a 109.56 inch ridgeline, leaving (180 − 109.56) ÷ 2 = 35.22 inches of horizontal run per side. The rise is 35.22 × tan 30° = 20.33 inches, the suspension length is 35.22 ÷ cos 30° = 40.67 inches, and the arc solution gives 31.28 inches of sag. Anchor height is 18 + 20.33 + 31.28 = 69.61 inches, or about 5 feet 10 inches.
Why an Uneven Hang Is Not Computed Here
The relation above splits the load evenly because both lines pull at the same angle. Attach one end higher than the other and that stops being true: the shallower line takes a larger share of the load and the steeper one a smaller share, and the shallower line is the one already at the bad end of the sine curve. Using the symmetric formula on an uneven hang therefore returns a force that is too small, on the side most likely to fail.
Producing a second number in the same confident styling would be worse than producing none. The tool declines instead. If your anchors are at different heights, the practical route is to adjust the suspension so both lines end up at the same angle, or to size the hardware from the shallower side treated on its own with a proper free-body diagram.
The Force Here Is Static, and You Are Not
Every number this page prints is for a body already at rest in the hammock. Getting in is not that. Sitting down, rolling over, or dropping the last few inches into the fabric accelerates your mass, and accelerating a mass on a line raises the tension above the static value — the point HyperPhysics makes plainly in its note on lifting a mass, where tension equals weight only when acceleration is zero. A person flopping into a hammock can easily generate a peak load of twice the static figure, and a bounce or a swing can go higher still.
This matters because working load limits are a fraction of breaking strength precisely to absorb that variation, and a shallow hang has already spent the margin. A 5 degree hang at 205 pounds is a static 1,176 pounds per anchor before anyone has moved. Add a dynamic multiple and anything without a published rating is entirely unknown.
What the Calculation Cannot See
Trees are the usual anchors and they are not engineering components. A tree that looks sound can be hollow, root-damaged, dead on one side, or holding a heavy dead limb above the hammock. Diameter is a weak proxy for strength, and species, age, soil and lean all matter. A branch is usually weaker than the trunk by a wide margin. Our tree diameter calculator and tree height calculator measure trees; neither of them, and not this page, assesses whether one will hold a load.
Strap width is the other thing the formula does not see. A narrow cord under high tension cuts into bark and into the cambium layer underneath, which can girdle and kill a tree over time; wide webbing spreads the same force. That is why land managers and organisations such as Leave No Trace ask hammock users to use wide tree-friendly straps, and why some sites prohibit hanging altogether. Check the rules of the place you are in before you hang anything.
Then there is the hardware. Climbing-rated carabiners and slings carry a published strength marked on the item and backed by a standard. Hardware-store snap hooks, S-hooks, screw eyes and generic carabiners frequently carry no rating at all, or carry one intended for holding a gate closed. If your weakest component has no published working load limit, the comparison in this tool cannot be made, and the honest reading of that is not that it is fine. Our factor of safety calculator covers the ratio itself, and the tension force calculator handles the general loaded-line case.
Finally, the fall zone. Anchor height, ground surface and what is underneath decide the consequence of a failure rather than its likelihood. A hammock over rock, over a fire ring, or high off the ground turns a component failure into a serious injury.
Arb Digital builds calculators that name the model, cite the source and refuse the cases they cannot do properly. Browse the library, or tell us what your readers keep getting wrong.
Browse Free Tools Talk To Arb DigitalCommon Mistakes to Avoid
- Hanging tight and flat because it looks neat. A shallow angle multiplies the load enormously and also gives a worse lie in the hammock. It is the single most common error.
- Assuming each anchor takes half your weight. At 30 degrees each anchor takes all of it, and below that, more.
- Using hardware with no published rating. A snap hook that holds a gate shut is not a load-rated connector, and this tool cannot compare against a rating that does not exist.
- Treating the calculated force as the peak. Every figure here is static. Getting in, rolling and swinging all add a dynamic multiple on top.
- Judging a tree by its diameter. Hollow trunks, dead limbs overhead, shallow roots and rot are invisible to a tape measure and are outside this calculation entirely.
Related Free Tools From Arb Digital
Work the general loaded-line case with the tension force calculator, explore the ratio between load and rating with the factor of safety calculator, look at how a suspended line hangs under its own weight with the catenary curve calculator and the cable sag calculator, and measure the trees themselves with the tree diameter calculator and tree height calculator. The rest of the library is in the free online tools hub.
Frequently Asked Questions
Far more than half the load. The static relation is force equals total weight divided by twice the sine of the hang angle. At 30 degrees each anchor carries the full weight; at 15 degrees about 1.93 times it; at 5 degrees about 5.74 times it. As the angle approaches zero the force grows without limit.
Because it is the conventional starting point among hammock campers, and because at 30 degrees the arithmetic is clean: the sine is exactly one half, so each anchor takes exactly the total weight. It is a convention rather than a rule, and this tool lets you set any angle and see the consequence.
No, and it will not. It reports what a static force balance returns for the numbers you entered. Tree health, hardware rating, strap width, anchor condition, the fall zone and the dynamic loads of getting in are all outside the model, and no output here should be read as approval.
Because the symmetric relation splits the load evenly only when both lines pull at the same angle. With anchors at different heights the shallower line takes a larger share and the formula understates it, in exactly the case most likely to fail. The tool declines rather than producing an optimistic number.
Because strength is a property of a specific product, and a figure typed from memory into a load calculation is worse than no figure. Read the working load limit off the component or its manufacturer documentation and enter it. If it has no published limit, that absence is the finding.
No. Every figure here is static, meaning a body already at rest. Sitting down, rolling over and swinging accelerate your mass and raise the line tension above the static value, often substantially. Treat the calculated number as a floor, not a peak.
It is mostly about the tree, and it matters. Narrow cord under high tension cuts through bark into the living layer underneath and can girdle a tree over time, which is why wide tree-friendly webbing is asked for by land managers and outdoor organisations. Some sites prohibit hanging entirely, so check the local rules first.
The force relation is the same, but the anchor question is completely different. Fixing into plasterboard, a stud, a joist, a fence post or a balcony rail is a structural question about that building element, and the loads calculated here are large enough that it should be treated as one rather than guessed at.
This page is a planning and teaching calculation only. It applies a simplified static model, it is not an engineering assessment, and no output from it states or implies that any hammock, anchor, tree or item of hardware is safe or strong enough. Read working load limits from your own components, treat every calculated force as a static floor rather than a peak, and where a hang depends on a tree or a building element, have somebody qualified look at it.
