Skeletal Muscle Mass Index (SMI) Chart: What's a Healthy Range by Sex?

Key takeaways

• SMI = appendicular (limb) muscle mass in kg ÷ height in m². A different whole-body % version (Janssen et al.) uses a different scale — check which one your device reports before comparing to any chart.
• Low-muscle cutoffs: AWGS 2019 flags below 7.0 kg/m² (men) and 5.7 kg/m² BIA / 5.4 kg/m² DXA (women); EWGSOP2 flags below 7.0 kg/m² (men) and 5.5 kg/m² (women) by DXA.
• Worked example: 22 kg of limb muscle at 1.75 m tall = 22 ÷ 3.06 ≈ 7.2 kg/m² — just above the men's cutoff, with little margin.
• Rule of thumb: sitting within about 0.3-0.5 kg/m² of your sex's cutoff is a "monitor closely" zone, not an automatic pass/fail line.
• Skeletal muscle mass is commonly reported to decline roughly 3-8% per decade after age 30, accelerating past 60 — a cited range, not a fixed rate for any one person.

"Do I have enough muscle?" is a fair question — and BMI can't answer it, because it can't tell muscle from fat. Skeletal muscle mass index (SMI) is the number clinicians actually use to flag low muscle mass (sarcopenia). This guide gives you the established reference cutoffs by sex, shows you how to calculate SMI with a worked example, explains how it differs from FFMI so you don't confuse the two, and covers what actually moves the number — age, training, and how fast realistic gains happen.

What is skeletal muscle mass index (SMI)?

SMI is a size-adjusted muscle score that lets a tall person and a short person be compared fairly, the same way BMI size-adjusts weight — except SMI isolates muscle instead of lumping in fat. The dominant clinical definition uses appendicular skeletal muscle mass — the lean muscle in your arms and legs, measured by DXA or bioelectrical impedance (BIA) — divided by your height in metres squared:

SMI = appendicular skeletal muscle mass (kg) ÷ height (m)²

A second, older definition (from Janssen and colleagues) expresses whole-body skeletal muscle as a percentage of body mass. It's a different scale with different numbers, so the single most important habit is to check which definition your scale or clinic report is using before you compare against any chart. Confusing the two is the single most common reason someone misreads their own result.

What is a healthy SMI by sex? (reference cutoffs)

There is no single "healthy" SMI number — instead, the medical consensus defines a low-muscle cutoff, the point below which muscle mass is considered low for age, and staying comfortably above it is the practical target. The two most widely cited guidelines are the Asian Working Group for Sarcopenia (AWGS 2019) and the European Working Group on Sarcopenia in Older People (EWGSOP2, 2019). Their appendicular SMI cutoffs for low muscle mass are:

Source: AWGS 2019 consensus (Asian Working Group for Sarcopenia) and EWGSOP2 2019 consensus (European Working Group on Sarcopenia in Older People). Cutoffs are commonly-cited reference thresholds for identifying low muscle mass; they are not a target score, and diagnosing sarcopenia also requires low muscle strength or physical performance, assessed separately from SMI.

Three things to read from this table. First, the threshold depends on the measuring device — a BIA scale and a DXA scan don't use the exact same women's cutoff, so don't mix them. Second, these numbers describe the floor, not a goal: the guidelines were built and validated mainly to catch age-related decline in older adults, so a young, healthy, untrained adult can sit close to the floor without having clinical sarcopenia. Third, a well-trained lifter of either sex typically sits several kg/m² clear of these cutoffs — the numbers matter most as a monitoring tool once you're past midlife, or if you're recovering muscle after an illness, injury, or extended layoff.

How do you calculate your SMI?

You calculate SMI in two steps once you have a muscle reading: square your height, then divide. You need two numbers: your appendicular (limb) skeletal muscle mass in kilograms and your height in metres. A DXA scan or a body-composition scale (InBody, Tanita, or a home BIA scale) will report the muscle figure; then:

• Step 1 — Square your height in metres. Example: 1.75 m → 1.75 × 1.75 = 3.06.
• Step 2 — Divide limb muscle mass by that. Example: 22 kg ÷ 3.06 = ≈ 7.2 kg/m².
• Step 3 — Compare to the cutoff for your sex and the device you used (from the table above).

In that example, a 1.75 m man with 22 kg of limb muscle scores 7.2 kg/m² — just above the men's 7.0 cutoff, with little margin. A second example shows why margin matters: a 1.60 m woman with 15 kg of limb muscle scores 15 ÷ (1.60 × 1.60) = 15 ÷ 2.56 ≈ 5.9 kg/m², clearly above both the AWGS BIA cutoff (5.7) and DXA cutoff (5.4) — a comfortable buffer, not a borderline reading. Because these are estimates, treat a single reading as a range and re-check the trend over time rather than reacting to one decimal.

What's a simple threshold you can actually use?

A practical rule of thumb: if your SMI sits more than about 1 kg/m² above your sex's cutoff, treat it as a comfortable margin and check again in a few months; if it's within roughly 0.3-0.5 kg/m², treat that as a "monitor closely" zone and recheck sooner, ideally with a consistent method and matched conditions; if it's below the cutoff, that's worth discussing with a clinician, especially alongside grip strength or a slow walking pace, since sarcopenia diagnosis needs more than the muscle number alone. This is a tracking heuristic to help you decide how often to remeasure — not a clinical protocol, and not a substitute for the guideline's full diagnostic criteria.

SMI vs FFMI — what's the difference?

SMI and FFMI measure different slices of your body, built for different jobs. SMI isolates skeletal muscle — clinically, just the arms and legs — and exists to screen for low muscle mass. FFMI (fat-free mass index) uses your entire fat-free mass, which includes muscle, bone, organs and water, and exists to gauge overall muscularity and training progress. People mix these up constantly, but the numbers and cutoffs aren't interchangeable:

Because FFMI includes bone, water and organs, its numbers run higher than SMI, and its reference ranges — including the widely cited ~25 natural-muscularity ceiling from Kouri et al. (1995) — don't apply to SMI at all. If you're tracking training progress rather than screening for low muscle, FFMI percentiles by sex is usually the more useful number, since it reflects total lean mass rather than just limb muscle. Use the right metric for the right question: SMI to check you're clear of a clinical floor, FFMI to gauge how muscular you actually are.

Does skeletal muscle mass decline with age, and should you worry?

Yes, skeletal muscle mass declines with age for almost everyone — the honest question isn't whether it happens, but how fast, and how much of it you can control. Sarcopenia and aging research commonly cites a decline on the order of roughly 3-8% per decade after about age 30, with the rate accelerating past age 60, though the exact figure varies widely by study population, measurement method and individual training history — treat that range as a general estimate, not a lab-derived constant. This is also why the AWGS 2019 and EWGSOP2 cutoffs exist in the first place: SMI is the number that turns "getting older" into something measurable and, to a meaningful degree, actionable. Resistance training and adequate dietary protein are the two interventions most consistently associated with slowing this decline — they don't stop it, but a lifelong lifter in their 60s commonly carries meaningfully more appendicular muscle than a sedentary peer, which is the entire practical point of tracking SMI before you're anywhere near a diagnostic cutoff. For more on how body composition norms shift with age generally, see our body fat percentage by age guide.

How can you increase your SMI, and how fast is realistic?

You increase SMI the same way you build any muscle — progressive resistance training plus adequate protein — and the realistic pace is slower than most people expect, especially past year one. A commonly cited rule-of-thumb muscle-gain model, popularized by strength coaches rather than a clinical SMI study, suggests a male training novice can add roughly 0.5-1 kg of total muscle per month in a consistent first year, tapering to about 0.25-0.5 kg per month by year two as the easy neuromuscular gains fade; women's rates commonly run roughly half that. Appendicular (limb) muscle is generally estimated to represent a large majority of total skeletal muscle mass, so most of that gain does show up in your SMI numerator — for a mid-height adult, that works out to very roughly 0.3-0.6 kg/m² of SMI gained in a genuinely productive first training year, and progressively less after that as you approach your individual ceiling. Two honest caveats: this estimate is a planning heuristic built by translating general muscle-gain figures into an SMI-shaped number, not a peer-reviewed finding about SMI itself, and a chunk of any early "SMI gain" measured by BIA is really measurement noise and water-weight shift rather than new tissue — which is exactly why the trend over months matters more than any two consecutive readings.

How can you track your muscle at home?

DXA is the reference method but means a clinic visit; for everyday tracking, a BIA scale or a photo-based estimate covers you between scans. Your practical options:

• BIA scale (InBody, Tanita, Renpho, etc.): estimates skeletal muscle mass from electrical impedance; convenient but shifts with hydration and time of day — see how BIA accuracy compares to a photo estimate in a real head-to-head test.
• Photo-based AI (e.g. Bodilab AI): estimates lean mass and per-muscle detail from a single photo, so you can watch whether muscle is holding or growing week to week — no equipment beyond your phone. See the best AI body fat apps for how these tools compare.
• DXA at milestones: use it occasionally for an accurate absolute value, then track the trend in between with whichever fast method you prefer.

Whatever method you use, consistency matters more than precision: same device, same conditions, same time of day. A repeatable weekly reading tells you more about whether your training is working than one precise-but-isolated measurement — and if your number ever sits near a sarcopenia cutoff, consistency is also what tells you whether that reading is real or just noise.

Frequently asked questions