STC vs Rw vs OITC: Sound Ratings Compared (With Examples)

STC, Rw and OITC measure different things. Compare test methods, target values by room type, and why the numbers are not interchangeable.

Last updated: November 2, 2026

Acoustic Doors · Last updated: 2 November 2026 · Jusen Doors Technical Team · Reviewed by Jusen Doors Engineering Team

STC vs Rw vs OITC: Sound Ratings Compared (With Examples)

Quick answer: STC, Rw and OITC are single-number sound ratings built for different jobs. STC is the North American laboratory classification weighted mainly around speech frequencies; Rw is the international weighted sound reduction index from ISO testing; OITC places more emphasis on low-frequency transportation noise. They cannot be converted by a universal formula. Buy the rating system named in the project specification and compare complete operable assemblies.

STC: speech privacy in North American specifications

Transmission loss measured to ASTM E90 is classified to STC using ASTM E413. The contour and frequency range make STC useful for offices, hotels and dwellings where speech privacy is a principal goal. Its limitations appear at bass-heavy sources: a door can hold an acceptable STC while passing noticeable low-frequency energy. For music, plant or aircraft/traffic problems, inspect the transmission-loss curve.

Rw: the ISO laboratory rating

ISO 10140 measurements are rated to Rw under ISO 717-1, often with C and Ctr spectrum adaptation terms. Rw is common in European, UK, Middle Eastern and Australasian specifications. The presence of adaptation terms matters: Rw + Ctr is a different comparison basis from bare Rw, especially for traffic. Door reports must state seals, frame, hardware and operating condition just as in ASTM work.

OITC: outdoor-indoor and low-frequency sources

OITC, classified under ASTM E1332 from transmission-loss data, is designed for exterior noise sources including aircraft, rail and road traffic. It extends attention to lower frequencies than STC. It is most often used for facade elements, exterior doors and windows rather than ordinary internal speech privacy. A product's OITC is commonly lower than its STC; that does not mean the product got worse, only that the rating is answering a harder low-frequency question.

Planning ranges without false equivalence

For early budgeting, hollow interior leaves often sit in the low-20 range under either STC or Rw reporting, solid standard doors commonly in the high-20s to mid-30s, and tested acoustic doorsets from the mid-30s upward. These bands help orientation only. No responsible buyer should write 'Rw 38 = STC 38' into a contract. Ask the supplier for the actual report in the specified system and to identify whether the assembly was operable.

Select by room and noise source

Hotel guest rooms, apartments and offices need speech privacy plus impact/flanking control from walls and corridors. Clinics need speech confidentiality. Music, cinema and plant rooms need low-frequency curves and often double seals or lobby arrangements. Start with source and receiver criteria from the acoustic consultant, then select door, wall, vent and junction details together. A premium leaf inserted into a weak frame/wall junction will not rescue the room.

Specification checklist: what to confirm before ordering

Rating system named in the specification (STC, Rw or a field metric), with no informal conversions.
Laboratory evidence for the complete operable assembly, including frame and seals.
Wall, junction, duct and other flanking paths reviewed with the door selection.
Threshold or drop-seal detail coordinated with flooring and accessibility.
Adjustment and seal replacement included in the maintenance plan.

Related guides

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FAQs

Can I convert Rw to STC by subtracting one?

No reliable universal conversion exists. Values can coincidentally be close, but contract evidence should be in the specified system.

Is OITC better than STC?

It is more appropriate for many exterior low-frequency sources, while STC is aimed more at speech. Better depends on the noise problem.

Why does field performance differ from all three ratings?

Laboratory ratings suppress flanking; buildings add wall junctions, ducts, frame cavities and installation gaps.

Data note: Figures described as typical, common or planning ranges are industry budgeting ranges with the stated assumptions. Building-code duties, tested scope and final quotations depend on destination, selected construction and order schedule.