Hong Life CalculatorsUnderstanding the hammock hang calculator — concept and principle
This calculator tells you how high to fix hammock straps on two trees or posts, how much tension each strap carries and how hard each anchor is pulled sideways, from the distance between the anchors, the hang angle and your weight. Use it before hanging a hammock to choose strap height and check that straps and anchors are strong enough.
How it is calculated
The hammock and straps are modelled as two straight lines from the anchors down to the sitting point, each at angle θ below horizontal.
- Strap height = sit height + (distance ÷ 2) × tan θ.
- Tension in each strap = W ÷ (2 × sin θ), in kgf; × 9.80665 for newtons.
- Sideways pull on each anchor = W ÷ (2 × tan θ).
- Line length from anchor to sitting point = (distance ÷ 2) ÷ cos θ.
The principle
This is the classic statics problem of a weight hung from the middle of a rope. At the sitting point, the two lines must hold up your weight together, so their vertical components add up to W: 2T sin θ = W. The shallower the angle, the smaller sin θ, and the larger the tension must be to provide the same upward force. At 30° each strap carries exactly your weight; at 15° about twice it; a nearly flat line would need enormous tension. The horizontal parts cancel each other at the hammock but pull the trees towards each other.
Worked example
Default inputs: anchors 4.5 m apart, hang angle 30°, sit height 0.45 m, person 80 kg.
- Strap height = 0.45 + 2.25 × tan 30° = 0.45 + 1.30 = 1.75 m (5.7 ft).
- Tension = 80 ÷ (2 × 0.5) = 80 kgf = 785 N, which is 1× body weight.
- Sideways pull = 80 ÷ (2 × 0.577) = 69 kgf.
- Line length = 2.25 ÷ cos 30° = 2.6 m.
| Hang angle below horizontal (°) | Strap height on each anchor (m) |
|---|---|
| 7.5 | 0.75 |
| 15 | 1.05 |
| 22.5 | 1.38 |
| 30 | 1.75 |
| 37.5 | 2.18 |
| 45 | 2.7 |
| 60 | 4.35 |
How to read the result
A hang angle of about 30° is a common recommendation because it keeps tension equal to body weight and gives a comfortable sag. Choose straps, carabiners and hardware rated well above the tension shown, because sitting down suddenly or bouncing adds load. A real hammock body sags in a curve, so treat the strap height as a starting point and adjust after a test sit.
Common mistakes
- Pulling the hammock tight and flat, which multiplies the tension.
- Using rope that bites into bark instead of wide tree straps.
- Measuring the distance between tree centres when the straps sit on the bark.
- Forgetting that two people double the load.
Frequently asked questions
What is the best angle to hang a hammock?
About 30° below horizontal is commonly recommended; at that angle each strap holds your body weight.
How high should hammock straps be?
For 4.5 m between trees and a 30° hang, about 1.75 m with a 45 cm sit height.
Why is a tight hammock dangerous?
Flat lines need much more tension to hold the same weight, which can break straps or anchors.
Sources: Standard statics: equilibrium of a load hung at the midpoint of two symmetric lines (e.g. R. C. Hibbeler, Engineering Mechanics: Statics) · Standard gravity 9.80665 m/s² (CGPM 1901)