How accurate is this STC estimate?

Treat it as a rough rule-of-thumb only, not a certified value. It is a mass-law-based industry estimation formula, not an ASTM E90-standardized predictive method, and it ignores the coincidence-effect dip, frequency-dependent interlayer behavior, and installation effects that all influence a real assembly's measured STC.

Where does the interlayer/gap bonus (R1) value come from?

It's an empirical adjustment for how much the interlayer or air/gas gap configuration improves on simple mass-law behavior — pull it from manufacturer data or published assembly comparisons for your specific makeup rather than assuming a default.

Does it make any difference that the two panes are different thicknesses?

Not to this formula. It adds the two surface densities and takes the logarithm of the total, so 15 + 5 kg/m² returns exactly the figure 10 + 10 does — 35.6 with a bonus of 5, either way round, and 18 + 2 lands there too. Unequal panes are one of the few genuinely effective moves in glazing acoustics, because each thickness has its own coincidence frequency and staggering them stops both leaves going transparent to sound at the same pitch; none of that reaches the arithmetic here, and the only place asymmetry can enter is the bonus you type in yourself. Mass is not a fast lever either: doubling the total glass, 20 kg/m² up to 40, buys about four points (13.5 × log10 2), while the bonus field alone spans ten. So if a choice between two makeups turns on a point or two, this page cannot settle it — tested ratings for the actual build-ups can.

The panes are 6 mm each — do I type 6?

No. The fields want mass per square metre, not thickness and not the weight of the finished unit. Ordinary soda-lime float glass runs about 2.5 kg/m² per millimetre of thickness, so 6 mm is 15 kg/m² and 10 mm is 25. Enter 6 and 6 and, at the default bonus of 5, you get 32.6 where 15 and 15 gives 37.9 — five points adrift, and silently, because 6 is a perfectly legal entry. For a laminate, roll both glass plies into a single pane figure: a 6 mm + 6 mm laminate is about 30 kg/m², the 0.76 mm PVB layer adding roughly another 0.8 kg/m², since the interlayer earns its place by damping rather than by weight and that belongs in the bonus field. Switched to imperial the two pane fields read lb/sq ft — 6 mm glass is roughly 3.1 — while the bonus stays in decibels in both systems, being an adjustment to the answer rather than a quantity to convert. Each pane field takes 2 to 40 kg/m² (0.41 to 8.19 lb/sq ft), which caps one pane at around 16 mm of glass; anything you type outside that is clamped to the nearer end, with a notice saying so.

If I glaze exactly this makeup, will the window perform at the number?

Rarely, and the shortfall is usually nothing to do with the glass. This is a figure for the glazing alone. What actually gets built is glass plus frame, plus the seal between frame and reveal, plus a sash and its weatherstripping if the window opens, and sound takes whichever path is weakest. Gaps are the brutal case: if one per cent of the opening is effectively open, a hundredth of the sound comes through it unimpeded, and a hundredth is 20 dB — so that one path pins the whole opening near 20 dB of transmission loss whatever the glass would have managed on its own. Background and trickle vents, sliding sash meeting rails, perimeter voids left unfoamed and a sealant bead that skipped the head all do precisely this. And where a number has to be met rather than aimed at — a planning or permit condition on internal noise, a bedroom facing a rail line, a room being built to a spectrum — this estimate has stopped being the right instrument well before that point. Outdoor noise carries far more low-frequency energy than the source spectrum an STC number is weighted for, which is why traffic- and aircraft-facing glazing is commonly compared on OITC as well; sizing that glass is work for an acoustic consultant reasoning back from the internal level across the whole facade, not a mass-law rule of thumb reasoning forward from two panes.

Materials & Quantities

Acoustic Laminated Glass STC Rating Estimator

Estimate an approximate STC (Sound Transmission Class) rating for a laminated/insulated glass makeup, from pane mass and interlayer/gap bonus.

Answers as you typeNo submit button
Every formula citedNamed published standards
Calculated in your browserNo account, nothing uploaded

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Market

Imperial · sales tax

Pane 1 Surface Density

The mass per unit area of the first glass pane.

For monolithic glass, surface density ≈ thickness (mm) × 2.5 kg/m² per mm, per standard soda-lime glass density.

Pane 2 Surface Density

The mass per unit area of the second glass pane.

Mass is what stops airborne sound across most of the range, which is why the second pane's substance matters more to the result than any coating on it. But mass alone does not describe a glazed unit: the cavity between the panes and whether either is laminated move the answer more than a small change here does, and a laminated interlayer damps the coincidence dip that mass cannot touch. Treat this as one term of several.

Interlayer/Gap Configuration Bonus (dB, R1)

An empirical bonus reflecting the acoustic benefit of the interlayer or air/gas gap between the panes.

Laminated PVB interlayers and wider, dissimilar-thickness air gaps typically justify a larger bonus than a simple monolithic or symmetric IGU makeup — this value should come from manufacturer data or published assembly comparisons, not guessed.

Estimated STC rating

36 STC (estimated)

Low confidence

This is an engineering rule-of-thumb estimate ONLY, not a certified rating — it ignores the coincidence-effect dip, frequency-dependent interlayer behavior, and installation effects. Always specify and verify acoustic performance using the manufacturer's actual ASTM E90 lab-tested STC value for your exact assembly, never this estimate, for any acoustic-critical project.

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

Mass-law-based estimation rule of thumb: STC ≈ 13.5×log10(M1+M2) + 13 + R1, where M1/M2 are pane surface densities (kg/m²) and R1 is an empirical bonus for the interlayer/air-gap configuration — this is a widely-used industry estimation formula, NOT an ASTM E90-standardized predictive method

Inputs used

Pane 1 Surface Density: 2.05 lb/sq ft
Pane 2 Surface Density: 2.05 lb/sq ft
Interlayer/Gap Configuration Bonus (dB, R1): 5

Final result35.56 STC (estimated)

Confidence note: This is an engineering rule-of-thumb estimate ONLY, not a certified rating — it ignores the coincidence-effect dip, frequency-dependent interlayer behavior, and installation effects. Always specify and verify acoustic performance using the manufacturer's actual ASTM E90 lab-tested STC value for your exact assembly, never this estimate, for any acoustic-critical project.

What this calculation does not cover

Two panes with a cavity between them are not one heavier pane. The pair resonates as a mass-spring-mass system, and around that resonance the unit transmits MORE sound than a single sheet of the same total weight. The frequency falls out of the two surface densities and the depth of the cavity, and a thermal IGU's usual 12 to 16 mm (0.47 to 0.63 in) gap puts it somewhere near 150 to 250 Hz — squarely where buses and lorries live. Cavity depth appears nowhere in this arithmetic; only the bonus you type can gesture at it, and a single number cannot express a dip.
A laminate earns its rating by damping, and damping is temperature-dependent. PVB, acoustic grades included, is characterised warm; it stiffens as it cools and hands back part of that interlayer bonus on a cold night — which is the night the traffic carries furthest against the quietest background. Whatever temperature the manufacturer's tested figure assumed travels silently into this estimate, and nothing on this page tracks it.

Add the equipment this sizes

This result is a specification — 36 STC (estimated) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

QtyItemPrice each ($)

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.1.1

Regulatory standards & verification citations1

Mass-law-based estimation rule of thumb: STC ≈ 13.5×log10(M1+M2) + 13 + R1, where M1/M2 are pane surface densities (kg/m²) and R1 is an empirical bonus for the interlayer/air-gap configuration — this is a widely-used industry estimation formula, NOT an ASTM E90-standardized predictive method

Which documents these citations point at

Standards referenced: ASTM E90 (ASTM International, United States).

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Isolating Sound Through a Partitionuses this calculator
A path-by-path hunt for flanking on a separating wall, from the perimeter bead to the plenum, before anyone argues about board.
Stopping Sound Through a Partition: Mass, Gaps and Decouplinguses this calculator
The open-area budget a partition gets to spend, what a doubling of board actually buys, and why the door decides the number.
Draught-Proofing and Secondary Glazing for Sash Windows

Called something else where you work? Insulating glazing unit — the term in each market, how close the equivalence really is, and the standard that governs it.

Still deciding? Acoustic Glazing vs Treating the Wall — the factors that actually differ, with no invented prices.

How to calculate acoustic laminated glass STC rating estimator in 4 steps

Pane 1 Surface DensityThe mass per unit area of the first glass pane.
Pane 2 Surface DensityThe mass per unit area of the second glass pane.
Interlayer/Gap Configuration Bonus (dB, R1)An empirical bonus reflecting the acoustic benefit of the interlayer or air/gas gap between the panes.
Estimated STC ratingThe tool computes the estimated STC rating from those figures and shows the formula, its sources, and a confidence rating alongside it.

Estimated STC rating by pane 1 surface density

Page defaults, not your figures above.

Pane 1 Surface Density	Estimated STC rating (STC (estimated))
1 lb/sq ft	33.8
1.5 lb/sq ft	34.7
2 lb/sq ft	35.5
2.5 lb/sq ft	36.2
3 lb/sq ft	36.8
3.5 lb/sq ft	37.3
4 lb/sq ft	37.8

Frequently asked questions

How accurate is this STC estimate?: Treat it as a rough rule-of-thumb only, not a certified value. It is a mass-law-based industry estimation formula, not an ASTM E90-standardized predictive method, and it ignores the coincidence-effect dip, frequency-dependent interlayer behavior, and installation effects that all influence a real assembly's measured STC.
Can I use this number in a project specification or acoustic compliance submittal?: No — for any acoustic-critical project, specify and verify performance using the manufacturer's actual ASTM E90 lab-tested STC rating for your exact glass makeup, not this estimate.
Where does the interlayer/gap bonus (R1) value come from?: It's an empirical adjustment for how much the interlayer or air/gas gap configuration improves on simple mass-law behavior — pull it from manufacturer data or published assembly comparisons for your specific makeup rather than assuming a default.
Does it make any difference that the two panes are different thicknesses?: Not to this formula. It adds the two surface densities and takes the logarithm of the total, so 15 + 5 kg/m² returns exactly the figure 10 + 10 does — 35.6 with a bonus of 5, either way round, and 18 + 2 lands there too. Unequal panes are one of the few genuinely effective moves in glazing acoustics, because each thickness has its own coincidence frequency and staggering them stops both leaves going transparent to sound at the same pitch; none of that reaches the arithmetic here, and the only place asymmetry can enter is the bonus you type in yourself. Mass is not a fast lever either: doubling the total glass, 20 kg/m² up to 40, buys about four points (13.5 × log10 2), while the bonus field alone spans ten. So if a choice between two makeups turns on a point or two, this page cannot settle it — tested ratings for the actual build-ups can.
The panes are 6 mm each — do I type 6?: No. The fields want mass per square metre, not thickness and not the weight of the finished unit. Ordinary soda-lime float glass runs about 2.5 kg/m² per millimetre of thickness, so 6 mm is 15 kg/m² and 10 mm is 25. Enter 6 and 6 and, at the default bonus of 5, you get 32.6 where 15 and 15 gives 37.9 — five points adrift, and silently, because 6 is a perfectly legal entry. For a laminate, roll both glass plies into a single pane figure: a 6 mm + 6 mm laminate is about 30 kg/m², the 0.76 mm PVB layer adding roughly another 0.8 kg/m², since the interlayer earns its place by damping rather than by weight and that belongs in the bonus field. Switched to imperial the two pane fields read lb/sq ft — 6 mm glass is roughly 3.1 — while the bonus stays in decibels in both systems, being an adjustment to the answer rather than a quantity to convert. Each pane field takes 2 to 40 kg/m² (0.41 to 8.19 lb/sq ft), which caps one pane at around 16 mm of glass; anything you type outside that is clamped to the nearer end, with a notice saying so.
If I glaze exactly this makeup, will the window perform at the number?: Rarely, and the shortfall is usually nothing to do with the glass. This is a figure for the glazing alone. What actually gets built is glass plus frame, plus the seal between frame and reveal, plus a sash and its weatherstripping if the window opens, and sound takes whichever path is weakest. Gaps are the brutal case: if one per cent of the opening is effectively open, a hundredth of the sound comes through it unimpeded, and a hundredth is 20 dB — so that one path pins the whole opening near 20 dB of transmission loss whatever the glass would have managed on its own. Background and trickle vents, sliding sash meeting rails, perimeter voids left unfoamed and a sealant bead that skipped the head all do precisely this. And where a number has to be met rather than aimed at — a planning or permit condition on internal noise, a bedroom facing a rail line, a room being built to a spectrum — this estimate has stopped being the right instrument well before that point. Outdoor noise carries far more low-frequency energy than the source spectrum an STC number is weighted for, which is why traffic- and aircraft-facing glazing is commonly compared on OITC as well; sizing that glass is work for an acoustic consultant reasoning back from the internal level across the whole facade, not a mass-law rule of thumb reasoning forward from two panes.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.