How This Calculator Works

This calculator measures the balance of explosive power between your two legs using the Single-Leg Vertical Jump. You jump as high as you can off one leg, then off the other, and enter both heights. From those two numbers the calculator produces a Limb Symmetry Index (LSI)A single percentage that expresses how closely your weaker leg matches your stronger leg. 100% means the two legs jumped identically; lower values mean a larger gap between them., identifies which leg is stronger and by how much, and places your result into one of three interpretation zones drawn from return-to-sport research.

Unlike a two-footed (bilateral) vertical jump, this test is not about how high you jump in absolute terms — it is about how evenly your two legs perform. A large side-to-side difference can flag an underlying imbalance, an unrehabilitated injury, or a training asymmetry, even in someone whose overall jump looks strong.

Step 1: Enter Your Details

The calculator needs just two measurements plus a unit selection:

• Left leg jumpThe height your jump-reach exceeded your standing-reach when pushing off the left leg only — not your total reach. — your best single-leg jump height pushing off the left foot, in centimeters or inches.
• Right leg jump — your best single-leg jump height pushing off the right foot, in the same way.
• Units — a single global toggle for the whole calculator (metric or imperial). Both inputs and all results adapt to the unit you choose.

Notice what is not required: no age, sex, or body mass. That is deliberate, and the reason is explained below under Why There Is No Power Estimate or Age Tier.

The Test Protocol

For a meaningful comparison, both legs must be tested the same way, in the same session, when fresh:

• Setup: Stand next to a wall on a level, non-slip surface with overhead clearance. Chalk the fingertips of the hand nearest the wall.
• Standing reach:The baseline. Stand flat on both feet for this measurement — it is subtracted from each single-leg jump to isolate jump height. Use the same baseline for both legs. With both feet flat and the arm fully extended overhead, mark the highest point your fingertips reach. This baseline is subtracted from both jumps.
• The single-leg jump:Balancing on one leg makes the countermovement harder to control than a two-footed jump, which is exactly why it exposes side-to-side differences. Balance on one leg, dip into a quick countermovement, and explode straight up off that single leg, marking the wall at the peak. The non-jumping foot should not touch down to assist.
• Test both legs: Take the best of three legitimate attempts on each leg. Alternate or fully rest between attempts so fatigue does not unfairly penalize whichever leg you test second.
• Keep conditions identical: Same footwear, same surface, same warm-up, same arm action on both sides. Any difference in method between legs shows up as false asymmetry.

How the Symmetry Index Is Calculated

The Limb Symmetry Index is simply the ratio of your weaker leg to your stronger leg, expressed as a percentage:

Because the smaller number is always on top, the result is always 100% or below. A score of 100% means both legs jumped exactly the same height. A score of 85% means your weaker leg reached 85% of your stronger leg's height — a 15% deficit. The calculator also reports the raw gap between the two legs in your chosen unit, and tells you which leg is stronger.

A note on convention.In clinical rehab, LSI is usually calculated as involved-limb ÷ uninvolved-limb, which can exceed 100% if the injured leg ends up stronger. This tool uses weaker ÷ stronger because it has no injury information about you. In a clinic, LSI is normally calculated as the injured limb divided by the healthy limb. Because this tool does not know whether you have an injury or which leg it would be, it uses the neutral weaker-over-stronger form, which works for general fitness and training comparisons.

The Three Symmetry Zones

Rather than the five performance tiers used elsewhere on this platform, this test uses a faithful three-zone clinical scale, because that is how symmetry is actually interpreted in the research literature. There is no honest way to grade a symmetry score into five athletic tiers, so we don't invent them:

• Symmetric — LSI ≥ 90% The most widely cited benchmark for "within normal limits." Originates from hop-test research and is the threshold most commonly used in return-to-sport criteria. : the two legs are within the range generally considered balanced.
• Mild Asymmetry — LSI 80–90% A noticeable but moderate gap. Often a target for corrective single-leg training to bring the weaker side up. : a moderate gap between the legs worth paying attention to.
• Marked Asymmetry — LSI < 80% A substantial difference. In a clinical setting this size of deficit is a common red flag in lower-limb screening. : a substantial difference between the legs.

The 90% cutoff traces back to the hop-test work of Noyes and colleagues (1991) and remains the most commonly used reference point in return-to-sport decisions. Treat these zones as general interpretation guidance, not a diagnosis — see the caveats below for why a single LSI number should never be the sole basis for any injury or readiness decision.

Why There Is No Power Estimate or Age Tier

If you have used the two-footed Vertical Jump calculator on this site, you may notice this one deliberately leaves out two things it has:

• No peak-power (watts) estimate.The Sayers equation was derived and validated on two-footed countermovement jumps. Applying it to a single-leg jump would report a number, but not a valid one. The Sayers power equation used in the bilateral calculator was developed and validated on two-footed jumps. Applying it to a single-leg jump would produce a misleading figure, so we omit it rather than show a number we cannot stand behind.
• No age-and-sex performance tiers.General-population single-leg vertical jump heights are not catalogued by age and sex the way two-footed jump norms are, so there is no honest table to grade an isolated single-leg height against. There is no established general-population table of single-leg jump heights by age and sex, so there is no honest standard to grade an isolated single-leg height against. The validated, meaningful output of this test is the symmetry between your legs — which is exactly what the calculator reports.

How to Read the Comparison Chart

The chart shows your two legs side by side as bars, in your selected unit. The stronger leg is shown in green; the weaker leg is shaded in the color of your symmetry zone (green if symmetric, orange for mild, red for marked). The visual gap between the two bars is your asymmetry — the bigger the gap, the lower your LSI. The reference table beneath restates the three zones and highlights the one your score falls into.

Why Leg Symmetry Matters

Most sport and everyday movement is single-legged — running, cutting, landing, and climbing stairs all load one leg at a time. A two-footed test can hide a weak side, because the stronger leg quietly compensates. Testing each leg on its own removes that masking effect and exposes imbalances a bilateral jump would never reveal.

Side-to-side asymmetry is most established as a tool in injury rehabilitation and return-to-sport decisions, particularly after knee injuries such as ACL reconstruction, where restoring symmetry is a common rehab milestone. Outside the clinic, large or persistent asymmetries are also of interest for performance and for guiding corrective single-leg training aimed at bringing the weaker side up to match the stronger one.

Important context: symmetry is only one piece of the picture. Some side-to-side difference is normal, and a perfectly symmetric pair of weak legs is not the same as a strong, balanced pair. Use this test alongside other measures, and mainly to track your own balance over time as you train.

Data Sources and Methodology

The symmetry framework and interpretation thresholds draw on the lower-limb function and return-to-sport literature:

• Noyes, F.R., Barber, S.D., & Mangine, R.E. (1991). Abnormal lower limb symmetry determined by function hop tests after anterior cruciate ligament rupture. The American Journal of Sports Medicine, 19(5), 513–518 — the foundational single-leg hop symmetry work behind the widely used limb-symmetry approach.
• Wellsandt, E., Failla, M.J., & Snyder-Mackler, L. (2017). Limb symmetry indexes can overestimate knee function after anterior cruciate ligament injury. Journal of Orthopaedic & Sports Physical Therapy, 47(5), 334–338 — the source of the caveat that a symmetry score can flatter the weaker limb when both legs have declined.
• Return-to-sport hop-testing references — the body of work establishing the single-leg hop and jump battery (single hop, triple hop, crossover hop, timed hop) and the ≥90% LSI benchmark commonly applied in clinical and athletic testing.
• ACSM's Guidelines for Exercise Testing and Prescription (11th Edition, 2021). Wolters Kluwer — standardized field-testing principles and interpretation.

A note on the thresholds: the 90% and 80% zone boundaries are conventions from return-to-sport research, not a single canonical normative table. They are a transparent, sensible reference for self-comparison and progress tracking — not figures that diagnose an injury or certify readiness to return to sport.

Limitations and Important Caveats

This calculator provides an estimate of balance between your legs, not a laboratory measurement or a clinical assessment. Several factors affect how to read it:

• LSI can flatter a weak pair of legs.Wellsandt et al. (2017) showed that after injury the "healthy" reference leg often weakens too, so a high symmetry score can still hide a real deficit relative to true pre-injury capacity. A symmetry score only compares your two legs to each other. If both legs have weakened — as often happens after injury — the LSI can look reassuringly high while real function is still reduced. A high LSI is not proof that either leg is strong.
• Not a return-to-sport test. Clinical return-to-sport decisions use a battery of tests, clinician judgment, and time since surgery — never a single symmetry number from a self-administered jump. Do not use this tool to decide whether to resume sport after an injury.
• Measurement accuracy. Balancing and landing on one leg is harder to measure cleanly than a two-footed jump. A jump mat or jump-and-reach device is more reliable than the chalk-and-wall method; keep the method consistent between retests.
• Test order and fatigue. Whichever leg you test second is at a disadvantage if you are tired. Rest fully between attempts, and consider alternating legs to keep the comparison fair.
• Some asymmetry is normal. Small side-to-side differences exist in almost everyone, including uninjured athletes, and limb dominance plays a role. A score just under 90% is not automatically a problem.
• Warm-up, surface, and footwear matter. A cold test, a soft or slippery surface, or different shoes on different days all distort the result. Use a brief dynamic warm-up, a firm non-slip surface, and consistent footwear across retests.
• Single-test snapshot. Sleep, recent training, and hydration all affect a single session. For tracking, retest under the same conditions every few weeks.

Disclaimer:
This calculator provides a general estimate of the balance between your two legs based on conventions from return-to-sport research. It is not a clinical assessment and must not be used to diagnose an injury, judge rehabilitation progress, or decide whether to return to sport or activity after an injury or surgery. Single-leg jumping and landing concentrate high forces on one knee, hip, and ankle; always warm up thoroughly, land softly with a bent knee on a forgiving surface, and stop immediately if you feel pain. This tool is for general informational purposes only and is not medical, rehabilitation, fitness, or training advice. Consult a qualified healthcare provider before performing maximal-effort or single-leg jump tests, especially if you have a pre-existing knee, hip, ankle, or back condition, are recovering from an injury, are over the age of 45, or have been sedentary for an extended period.