Anchor Force Calculator
In a V-shaped two-point anchor the load splits between the legs - but the wider the angle, the smaller that split. The vector math is one line; the consequences are not.
Result
| Included angle between the legs | Force per leg |
|---|---|
| 0° | 50% |
| 30° | 52% |
| 60° | 58% |
| 90° | 71% |
| 120° | 100% |
| 150° | 193% |
Above 120° each leg carries more than the full load; above 150° almost twice. Keep anchor angles narrow.
Reference physics for constructed anchors, ignoring friction, unequal leg lengths and stretch. Real anchor evaluation includes much more - this is not a substitute for qualified instruction.
How the calculation works
Equilibrium at the master point gives one line of vector math:
W is the load, θ the included angle between the legs. At 0° each leg carries 50%; at 60°, 58%; at 90°, 71%; at 120°, 100%; at 150°, 193%. The table in the results panel is the classic multiplier chart - the angle is the only variable that matters, which is why anchor building is about geometry first and gear second.
Above 120° each leg carries more than the full load; above 150° almost twice. Keep anchor angles narrow.
The physics and the rigging habits that follow from it are in the anchor angles guide. The force these legs have to catch comes from the fall factor calculator.
Planning estimate only - not safety advice.
Frequently asked questions
Why does a wide anchor angle multiply force?
Each leg must pull both downward and inward to keep the load point in equilibrium. The wider the V, the more of each leg's tension is spent fighting the other leg horizontally, so the tension must grow. At 120° the inward pull consumes the entire leg strength and each piece carries the full load.
What angle should I aim for?
Under 60° is the textbook target: each leg carries about 58% of the load or less. Up to 90° is still acceptable (71% per leg). Past 120° each leg carries more than the whole load alone - a wider-than-that anchor is worse than a single point.
Does this apply to multipoint anchors with three or more pieces?
The one-line math here is for two equal legs and one load point. More points change the geometry but not the principle: diverging directions waste force. Real systems also have friction, unequal leg lengths and stretch, which redistribute load in ways this model deliberately ignores.
What load should I enter?
For planning, climber plus pack - 80 kg is the standard reference mass. The model is static; real catches add dynamic overshoot, and hauling or hanging loads can exceed body weight. The calculator is about angles and ratios, not certification.