Ape Index, Explained
After reading this you can measure your wingspan, compute your ape index both ways it is quoted (as a difference and as a ratio), and read the result honestly against population norms.
What the ape index is
Your ape index compares the width of your outstretched arms to your standing height. Most people are close to a square: arms span roughly the same distance as height. Some people reach further than they stand. That surplus reach is what the index captures.
Take a climber who is 175 cm tall with a wingspan of 180 cm. Their arms reach 5 cm past what their height would predict. On a steep wall, that 5 cm can turn a lunge into a controlled move to the next hold. The same surplus helps a swimmer catch more water per stroke and a boxer land from outside an opponent's range.
The metric is descriptive, not predictive. A positive index is a small structural advantage in a few sports, nothing more. Technique, strength and training dominate.
When to use it, and when not to
Reach for the ape index when you want a single number for arm-to-height proportion: sizing yourself against climbing route betas, comparing two athletes, or tracking a growing junior whose arms and torso lengthen at different rates.
Do not use it as a talent filter. The difference between a +2 cm and a +6 cm climber is real but tiny next to years of practice. And do not compare indexes measured with different methods. A slouched height measurement or bent elbows during the span reading will move the number more than most genuine anatomical differences.
Small measurement errors dominate this metric. A 2 cm error in either height or span shifts your index by 2 cm, which is larger than the gap between an average person (about +1 cm) and someone with genuinely long arms (+5 cm). Measure twice.
The two formulas
The ape index is quoted two ways. The first and most common is a plain difference in length.
Here span is your fingertip-to-fingertip wingspan and height is your standing height, both in the same unit. The result is a signed length. Positive means your arms are proportionally long, negative means proportionally short, zero means square.
The second form is a ratio, which removes units and makes people of different sizes directly comparable.
A ratio of 1.0 is square. Above 1.0 means long arms. The two forms carry the same information for one person, but the ratio scales fairly across body sizes. A 5 cm surplus means more on a 150 cm frame than on a 200 cm frame, and the ratio reflects that: 155/150 \approx 1.033 versus 205/200 = 1.025.
Worked example with the demo numbers
Height 175 cm, wingspan 180 cm
- Difference form:
180 - 175 = 5cm. The index is +5 cm. - Convert to inches if you want it that way: 5 / 2.54 \approx 1.97 in, so just under two inches.
- Ratio form: 180 / 175 \approx 1.0286, which rounds to 1.029.
- Read it as a percentage over square: (1.0286 - 1) \times 100 \approx 2.86\% more reach than height.
So the demo athlete sits at +5 cm, or a ratio of 1.029. By the tool's own footnote that counts as genuinely long: +5 cm or more is at the upper end of the normal range.
To turn a ratio back into a difference, multiply your height by the ratio and subtract your height. For 175 cm at 1.029: 175 \times 1.029 - 175 = 5.08 cm. The small gap from 5 cm is rounding in the ratio.
Reading and interpreting your result
The population average is a slightly positive index, roughly +1 cm, or a ratio near 1.006. Most people fall within a band of about plus or minus 4 cm around that. The table below shows how a difference maps to a ratio at 175 cm height, so you can sanity check whichever form the tool reports.
| Difference (cm) | Difference (in) | Wingspan (cm) | Ratio | Reading |
|---|---|---|---|---|
| -5 | -1.97 | 170 | 0.9714 | Short reach |
| 0 | 0.00 | 175 | 1.000 | Square |
| +1 | +0.39 | 176 | 1.006 | Average |
| +5 | +1.97 | 180 | 1.029 | Long |
| +10 | +3.94 | 185 | 1.057 | Exceptional |
Notice that the same difference gives a different ratio at a different height. A +5 cm surplus is 1.029 at 175 cm but only 1.025 at 200 cm. If you compare yourself to a much taller or shorter person, use the ratio.
Watch how the ratio changes with height
The difference and the ratio are not interchangeable across body sizes. A fixed surplus in centimeters shrinks as a fraction when the person is taller. The widget below lets you hold a difference constant and slide height to see the ratio drift.
Common mistakes
Most bad ape index numbers come from measurement, not arithmetic. The formula is trivial. The reading against a wall is where errors creep in.
- Bent elbows
- If your arms sag or your elbows bend even slightly, you lose reach. A 3 cm loss here reads as a 3 cm smaller index, enough to move you from long to average.
- Rounded shoulders
- Pulling your shoulder blades forward shortens the span. Stand tall and reach evenly to both sides.
- Mixing units
- Measure both height and span in the same unit. A span in inches minus a height in centimeters is meaningless. Convert first: 1 in equals 2.54 cm.
- Comparing difference across heights
- A +6 cm friend who is 165 cm has a larger ratio (1.036) than a +6 cm friend who is 190 cm (1.032). Use the ratio when heights differ.
- Over-reading small numbers
- The gap between +1 and +3 cm is within the error of a wall measurement. Do not treat it as meaningful.
Related tools
If you climb, your ape index is one input among many when you read a route. Convert grades between systems with the Climbing Grade Converter so you can compare a French route grade to a V-scale boulder problem. For a different body-and-height calculation on the snow, the Ski Binding DIN Calculator turns weight, height, age, skier type and boot length into a release value.
Frequently asked questions
What is a good ape index for climbing?
Anything positive helps a little. The population average is about +1 cm. A value of +5 cm or more is genuinely long and is common among strong boulderers. But the effect is small compared to finger strength and technique, so a negative index is not a barrier.
How do I measure my wingspan accurately?
Stand with your back to a wall, arms horizontal at shoulder height, and reach evenly to both sides with straight elbows. Mark each middle fingertip and measure the distance between marks. Keep your shoulders relaxed and level. Take the reading twice and average them.
Is the ape index the same as arm span?
No. Arm span (wingspan) is the raw fingertip-to-fingertip distance, such as 180 cm. The ape index is that span compared to your height, either as a difference (+5 cm) or a ratio (1.029). The index only means something when both measurements are used together.
Can my ape index change over time?
Your bones stop growing in adulthood, so the underlying value is stable. In children and teenagers, arms and torso lengthen at different rates, so a junior's index can drift by several centimeters over a year or two. Posture and measurement technique cause most apparent changes in adults.
Why do some people quote a negative ratio, like 0.97?
A ratio below 1.000 means the span is shorter than the height, the same information a negative difference carries. At 175 cm height, a span of 170 cm gives a difference of -5 cm and a ratio of 0.9714. Both say your arms are proportionally short.
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