What is Mass Index?
The Mass Index watches the range of each bar, high minus low, and asks whether that range is currently wider than its own smoothed average. It adds up that comparison over the last Length bars and plots the total in its own pane. When ranges are expanding the total climbs; when they settle it falls back.
The Mass Index looks only at range, never at direction. It does not say whether a reversal will be up or down, and a rising reading is not a signal on its own.
How to use Mass Index
- Around the length. When the bar range is neither widening nor narrowing, each bar's ratio is close to 1, so the total sits near the Length setting, about 10 at the default.
- The reversal bulge. The reading the indicator's own description gives, attributed to Dorsey, is a bulge above 27 that then falls back through 26.5. It is taken as a warning that the current trend may reverse, whichever way it was going.
- Direction comes from elsewhere. Because the Mass Index has no direction, the bulge is usually read alongside a trend tool such as a moving average to judge which way the turn would go.
- Scale with the length. Each ratio sits near 1, so the total sits near the Length. At the default of 10, a reading of 27 would need ratios averaging 2.7, which is rare. The 27 and 26.5 levels only come into play with a longer sum, so judge bulges against the line's own history or lengthen the sum.
These are ways to read range expansion, not entry signals on their own.
Settings
| Setting | Default | What it changes |
|---|---|---|
| length | 10 | Bars whose ratios are added together. A longer sum moves more slowly and sits at a higher level; a shorter one reacts sooner. Minimum 1. |
The two 9-bar smoothings inside the calculation are fixed. Only the summing length can be changed.
Calculation
Each bar, the indicator smooths the bar range twice with a 9-bar EMA, divides the single smoothing by the double one, and sums that ratio over the last Length bars:
span = high - low
single = EMA(span, 9)
double = EMA(single, 9)
ratio = single / double
Mass Index = sum of ratio over the last 10 barsWhen the range is steady, the single and double smoothings agree and the ratio is about 1. When the range starts widening, the single smoothing rises first and the ratio climbs above 1; when it narrows the ratio drops below 1.
Each EMA is started from the simple average of its first 9 values, so the double smoothing appears after about 17 bars, and the sum needs a further Length ratios on top of that. At the default the first value arrives after roughly 26 bars. No levels are drawn on the pane.
Limitations
- No direction. A widening range in a rally and in a sell-off look the same, so it cannot say which way a turn would go.
- The classic levels do not fit the default. Because the total sits near the Length, the 27 and 26.5 thresholds are rarely reached at a length of 10. They need a longer sum, or levels taken from the chart itself.
- Range expansion is not always a reversal. Ranges also widen at the start of a strong trend continuation or around news, and the bulge can appear without any turn following.
- The live candle moves. The current bar's high and low can still change, so its value moves until that bar closes.
- It is not a strategy. It gives a warning, not an entry, exit, sizing or risk management.
Frequently asked questions
The Mass Index is a volatility indicator that compares the bar range, high minus low, with a smoothed version of itself and sums that comparison over recent bars. It rises when ranges are widening and falls when they settle.
The best-known reading is the reversal bulge, a rise above 27 followed by a drop back below 26.5, which is taken as a warning that the current trend may turn. The line sits near its length setting when ranges are steady, so at the default of 10 those levels are rarely reached. Lengthen the sum if you want to use them, or judge bulges against the line's own history.
Yes, one of them. The indicator declares a single input: length, the number of bars summed, default 10 with a minimum of 1. The two 9-bar EMAs inside the calculation are fixed. Open the indicator's settings on the chart to change the length.
No. Each value uses only that bar and the ones before it, so values on closed bars are not revised. The current candle's reading moves while its high and low are still forming and settles when it closes. Because the smoothing needs a starting point, loading older history recalculates it and values near the very start of the loaded range can shift.
No. It only measures range expansion. The direction of a possible reversal has to come from price itself or from a trend indicator.
Use the Add to chart button at the top of this page. It opens BTC/USDT on Binance in the Altrady Charts terminal with the built-in Mass Index already applied. On any other market, open the indicator picker on the chart and choose Mass Index from the Volatility group.