RSI Calculator
Reactive Strength Index calculator
Enter a jump height and ground contact time to get RSI instantly — plus DRI, the drop-height-aware reactive score co-developed with Lance Brooks. Free, no sign-up. Then see what the numbers mean.
Legacy RSI · Just Jump
Legacy RSI = (FT × 1.1119) ÷ CT
—
Legacy RSI
Just Jump-matched value
DRI · drop-height aware
DRI = JH ÷ (CT × √DH)
A live demo of exactly what a Plyomat jump mat computes on every rep — automatically, to 0.001 s, with no hand timing.
Learn what RSI means →The formulas
RSI, Legacy RSI & DRI
RSI (Reactive Strength Index) = jump height ÷ ground contact time. It's the 30-year industry standard for reactive strength — more height for less time on the ground means a stiffer, more elastic, more reactive athlete. It's the headline number for drop jumps and repeated hops.
Legacy RSI (Plyomat) = (flight time × 1.1119) ÷ contact time. It's a flight-time-based RSI that deliberately re-applies the old Just Jump System's flight-time inflation factor of 1.1119. Why does it exist? The Just Jump System over-reported flight time for years, so a generation of coaches built their historical jump data on those inflated numbers. Legacy RSI matches that value so coaches migrating from Just Jump keep continuity with their old data. Standard RSI (jump height ÷ contact time) is the accurate, modern default; Legacy RSI is for backward-compatibility only, and it sits on a different scale, so don't compare the two numbers directly.
DRI (Dynamic Rebound Index) = jump height ÷ (contact time × √drop height). Co-developed with Lance Brooks, DRI fixes RSI's biggest blind spot: drop height. A 1.8 RSI off a 30 cm box and a 1.8 off a 60 cm box are not the same performance, but classic RSI can't tell them apart. The √drop-height term keeps DRI roughly comparable across boxes, so it's better for return-to-play, progressing athletes to taller boxes, and longitudinal tracking.
Interpreting it
What is a good RSI score?
A rough drop-jump guide for jump-height-based RSI (m/s). Treat these as ballparks, not gospel — RSI shifts with the test, the drop height, and the population.
| RSI (m/s) | General level |
|---|
| < 1.5 | Developing / recreational |
| 1.5 – 2.0 | Solid, trained athlete |
| 2.0 – 2.5 | Very good |
| 2.5 – 3.0 | Excellent |
| 3.0 + | Trends toward elite jumping / sprinting athletes |
Use the trend, not the table. The same athlete tested on the same protocol over time tells you far more than a single number compared to a population average. Different drop heights and test types (drop jump vs 10-to-5 hop) produce different RSI ranges — which is exactly why DRI accounts for drop height. (For brand-new DRI there are no published population norms yet; use it to compare an athlete across drop heights and over time.)
Questions
RSI & DRI FAQ
How do you calculate Reactive Strength Index (RSI)?
RSI = jump height ÷ ground contact time. With consistent units (height in metres, contact time in seconds), a 0.40 m jump with a 0.20 s contact time gives an RSI of 2.0 m/s. Higher = more height for less ground time = more reactive.
What is a good RSI score?
It depends on the test, drop height, and athlete. As a drop-jump ballpark (m/s): under ~1.5 developing, ~1.5–2.0 solid, ~2.0–2.5 very good, ~2.5+ trending elite. Compare an athlete to their own baseline on the same test — that beats any population average.
What is DRI and how is it calculated?
DRI (Dynamic Rebound Index) = jump height ÷ (contact time × √drop height), co-developed with Lance Brooks. The √drop-height term makes reactive scores comparable across drop heights — something classic
RSI can't do.
Why is DRI better than RSI for drop jumps?
Classic RSI ignores the box you dropped from, so the same RSI from a 30 cm and a 60 cm box look identical even though they aren't. DRI's drop-height term keeps the score roughly scale-invariant, so it's more honest for return-to-play and tracking athletes as they progress to taller boxes.
What is Legacy RSI, and why does Plyomat have it?
Legacy RSI uses flight time ÷ contact time with the old Just Jump System's flight-time inflation (×1.1119) applied. The Just Jump System over-reported flight time for years, so coaches' historical data was built on inflated numbers. Legacy RSI matches those values so coaches moving from Just Jump keep continuity with their old data. Standard RSI (jump height ÷ contact time) is the accurate default; Legacy is for backward-compatibility only, and its scale differs, so don't compare the two directly.
Do I need special equipment to measure RSI?
You need accurate contact-time and flight-time measurement, which is hard to do by hand. A
contact mat like Plyomat times each contact to 0.001 s and computes RSI, DRI, RSQ, and Power Score live — no manual math, no stopwatch.
Stop calculating. Start measuring.
Plyomat computes RSI, DRI, the Reactive Strength Quadrant, and Power Score on every rep — automatically, to 0.001 s, on a portable mat. No hand timing, no spreadsheets.
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