How this calculator works
The model treats the hammock fabric as two straight halves meeting at the lowest point, with a structural ridgeline holding the ends apart. The sag is the height difference between that lowest point and the ends, found from the right triangle formed by half the fabric, half the ridgeline and the drop. The suspension runs from each hammock end to its anchor at the chosen angle, so its horizontal run is the anchor gap minus the ridgeline divided in two. From the same right triangle, the vertical rise is the suspension length times the sine of the angle. Each cord carries half the load, divided again by the sine of the angle, so shallow hangs pull much harder than steep ones.
Formula
Sag = square root of (half hammock length squared - half ridgeline squared). Suspension length per side = (anchor distance - ridgeline) / (2 x cosine of the hang angle). Anchor height = sit height + sag + suspension length x sine of the angle. In the reverse direction, sit height = anchor height - sag - suspension length x sine of the angle. Cord tension = weight x 9.80665 / (2 x sine of the angle), and the equivalent mass is weight / (2 x sine of the angle).
Worked example
With anchors 4.5 m apart, 3 m of fabric and a 2.49 m ridgeline, the sag is the square root of 1.5 squared minus 1.245 squared, or 0.84 m. At a 30 degree angle each suspension is (4.5 - 2.49) / (2 x 0.8660) = 1.16 m long. A 0.45 m sit height needs anchors at 0.45 + 0.84 + 0.58 = 1.87 m. An 80 kg load puts 785 N on each cord, equivalent to about 80 kg of hanging mass.
Advertisement
Frequently asked questions
Why is 30 degrees the recommended hang angle?
A hammock hung flatter feels more stable but multiplies the tension in the cords and the load on the trees. Thirty degrees is the widely used compromise between a comfortable lie and a safe load, and shallower angles should be treated as a warning sign.
What does the ridgeline actually do?
A structural ridgeline connects the two hammock ends and stops them spreading apart. That fixes the sag regardless of how far apart the trees are, which makes the hang consistent from site to site. Without a ridgeline the sag depends on the anchor distance.
Can I use this with webbing straps instead of cord?
Yes. The geometry and tension are the same for any suspension material, though the strength rating of the strap or cord must exceed the calculated tension with a generous margin. Tree protection straps are also required in many parks.
Why does the model ignore the curve of the body?
The two-straight-halves approximation is simple and matches a taut ridgeline setup closely enough for planning. A real hammock curves, and a person is not a point load, so check the finished hang by sitting in it before relying on the numbers.