Window Tint Guide: Understand
South Carolina's 27% Tint Rule, Explained With Examples
Most people hear that South Carolina allows 27 percent tint and assume any film labeled 27 percent or lighter is fine. The statute does not say that. It says the film and the glass it sits on must let through at least 27 percent of visible light together, and the glass always takes its share before the film does.
This guide shows how that combined number is worked out, why a film that sounds safe can read below the limit on a meter, and how to estimate the lightest film your particular glass can carry. The arithmetic takes about a minute once you see it.
The short answer
South Carolina's 27 percent rule means the film plus the factory glass must pass at least 27 percent of visible light combined. To estimate it, multiply the glass transmission by the film transmission: 80 percent glass with 35 percent film gives about 28 percent, which passes, while 70 percent glass with the same film gives about 24.5 percent, which fails. The film alone is never the whole answer.
Key points
- The statute measures the combined light transmission of the film with the factory glass, not the film's own rating.
- Combined transmission is roughly the glass percentage times the film percentage, so the result is always darker than the film alone.
- To find the darkest film your glass can take, divide 27 by the glass's own transmission: 27 divided by 75 means film of about 36 percent or lighter.
- Dark factory glass with no film on it is not a tint violation, but adding film over it brings the 27 percent test into play.
- Portable tint meters read the window as it is, film and glass together, so leave a margin rather than aiming exactly at 27.
The wording
What the Statute Actually Measures
Subsection (C) of S.C. Code § 56-5-5015 says film on the side windows must be nonreflective and 'the combined light transmission of the sunscreening device with the factory or manufacturer installed sunscreening material must not be less than twenty-seven percent.' Subsection (D)(2) uses the same words for the rear-most window.
Subsection (J) defines light transmission as the ratio of the visible light that passes through a product to the total light falling on it. So 27 percent means at least 27 of every 100 units of visible light have to make it through the window as it sits on the car, glass and film together.
The phrase factory or manufacturer installed sunscreening material matters. Automotive glass is rarely perfectly clear. Even untinted-looking glass absorbs and reflects some light, and many vehicles have a factory tint baked into the glass. The law counts that loss before the film gets any credit.
The math
How Film and Glass Combine
Light passing through two layers loses a share at each one. A good working estimate is to multiply the two percentages as decimals. Glass that passes 80 percent of light, covered by film that passes 35 percent, gives 0.80 times 0.35, or 0.28. That window reads about 28 percent, just above the line.
Reverse the calculation to find the darkest film a window can take: divide 27 by the glass's own transmission. If your glass passes 75 percent, 27 divided by 75 is 0.36, so film of about 36 percent or lighter keeps you legal on that glass. Real readings can drift a point or two from the simple product because of reflections between layers, which is one more reason to leave a margin.
Two things follow from the arithmetic. Any film makes the window darker than the film's label, never lighter. And the same film can be legal on one car and illegal on another, because glass varies from vehicle to vehicle and even window to window.
Find the glass number
Have the bare glass measured with a tint meter before any film goes on, or ask the installer to do it. Factory glass is not a fixed value you can look up for every model.
Divide 27 by it
Use the glass reading as a whole number. 27 divided by 78 is about 0.35, so 35 percent film is the darkest that glass can carry.
Step lighter for a margin
Choose the next lighter film rather than the exact cutoff. Meters, film batches and glass all vary slightly.
Check the result
After installation, a meter reading of the finished window should be at 27 percent or above. That reading, not the box, is what counts.
Factory glass
Why Glass Matters More Than People Expect
Federal glazing rules set a floor on how much light car glass must pass where the driver needs to see. In its 2012 rulemaking notice on Standard No. 205, the National Highway Traffic Safety Administration (NHTSA) described a 70 percent luminous transmittance requirement for glazing in areas requisite for driving visibility, and stated its position that on passenger cars all windows in the passenger compartment are requisite for driving visibility.
That means car glass can legally leave the factory at 70 percent. If your sedan's side glass is near that floor, the darkest film it can carry under South Carolina's rule is 27 divided by 70, or about 39 percent film. Glass that passes more light leaves more room for darker film.
Trucks, buses and multipurpose passenger vehicles are treated differently at the federal level: the same notice says their glazing is subject to the 70 percent test only as a windshield, beside the driver, or as the rear-most window when it is used for driving visibility. That is why many SUVs have dark privacy glass behind the driver from the factory, and why South Carolina's own exception for those windows is covered in a separate guide.
Privacy glass
Film Over Factory Privacy Glass
Subsection (A) says that if no after-factory film has been added to a window, the light transmittance rules do not apply. A pickup with dark factory glass in its rear doors is not breaking the tint law on that glass alone.
The picture changes the moment film goes on. Once a window has after-factory film, the combined reading of film plus that dark glass must reach 27 percent wherever the limit applies. On a pickup, the limit applies behind the driver, so even a light film over dark factory glass can push the reading under 27. Multiply it out: if the glass passes, say, 30 percent, a 70 percent film over it reads about 21 percent.
On a vehicle classified as a multipurpose passenger vehicle, the light transmittance limit does not apply behind the driver at all, so this problem is limited to the front side windows. Those front windows usually have clear glass, which is why they look lighter than the rear even when the film is the same.
Enforcement
How Meters Fit In
The statute does not say how compliance must be measured. In a 2012 opinion to the Holly Hill police chief, the South Carolina Attorney General's office noted that § 56-5-5015 does not dictate what device or method of proof should be used and does not exclude tint meters, cited cases from other states upholding portable meters, and left admissibility to the courts case by case.
That department described its own practice in the request: its meters were certified accurate to within plus or minus 2 percent, so it did not issue citations for readings of 25 percent or higher. That was one agency's policy, not a statewide rule, and nothing requires other officers to give the same allowance. Plan for a reading of 27 or better.
A meter reads the window as it is, so it captures glass, film and anything else in the light path. Dirt or a cracked film does not help, and a meter cannot tell what number was printed on the box.
Common mix-ups
Mistakes That Push a Window Under 27
- Choosing film by its label alone. A film rated near 27 percent will read darker once it is on glass.
- Stacking a new film over old film. The statute allows a single sunscreening device on those windows, and two layers multiply down quickly.
- Assuming every window on the car has the same glass. Rear glass and quarter windows can differ from the front doors.
- Matching the fronts to factory privacy glass in the rear. On most vehicles that match is not possible within the limit.
- Treating the sticker as proof of the reading. The certificate states the film's own percentage; a meter reads the combination.
On the rear-most window, film installed before January 1, 1993, that met the old 20 percent standard at the time is not a violation while that original film stays in place (subsection (D)(3)). Any replacement must meet the 27 percent combined rule.
| Glass passes | With 50% film | With 35% film | Darkest film for 27% combined |
|---|---|---|---|
| 85% | about 42.5% | about 29.8% | about 32% film |
| 80% | about 40% | about 28% | about 34% film |
| 75% | about 37.5% | about 26.3% (fails) | about 36% film |
| 70% | about 35% | about 24.5% (fails) | about 39% film |
| 30% (example of dark factory glass) | about 15% (fails where the limit applies) | about 10.5% (fails where the limit applies) | about 90% film, nearly clear |
Estimates using glass percentage times film percentage. Real meter readings can differ by a point or two. The 27% limit does not apply behind the driver on multipurpose passenger vehicles.
Not sure what your glass will allow?
We check the legal shade for your vehicle before installing, because factory privacy glass and tinted factory glass already reduce light. Book online or ask for a quote.
Common questions
Is 27 percent the film number or the window number?
The window number. Subsection (C) of the statute measures the combined light transmission of the film with the factory glass. A film rated 27 percent will read darker than 27 once it is on any real glass, so it would fail. The film has to be lighter than 27 percent for the finished window to reach 27.
How do I find out what my factory glass transmits?
Have the bare glass read with a tint meter before film goes on. Glass varies by vehicle, by window and by any factory tint in it, so a published number for your model is at best a guess. A careful installer measures first, then picks a film that leaves the finished reading at 27 percent or above with some margin.
Will an officer give me a couple of points of leeway on the meter?
Do not count on it. One South Carolina department told the Attorney General in 2012 that it did not cite readings of 25 percent or higher because its meters were accurate to plus or minus 2 percent, but that was its own policy. The statute sets 27 percent, and nothing requires every agency to allow the same margin.
Does the 27 percent rule apply to the back glass of an SUV?
Not if the vehicle is classified as a multipurpose passenger vehicle. Subsection (I) says the light transmittance requirement does not apply to windows behind the driver on MPVs, other trucks, buses and RVs. It does apply on pickup trucks and cars. The film still has to be nonreflective, not red, yellow or amber, and labeled with a certificate.
Sources
- S.C. Code Ann. § 56-5-5015, South Carolina Legislature (https://www.scstatehouse.gov/code/t56c005.php), accessed October 2026
- Federal Motor Vehicle Safety Standards; Glazing Materials, Notice of Proposed Rulemaking, 77 FR 37478 (June 21, 2012), NHTSA via Federal Register (https://www.federalregister.gov/documents/2012/06/21/2012-14996/federal-motor-vehicle-safety-standards-glazing-materials), accessed October 2026
- Opinion to Chief Robert H. Wunderlich on the use of battery-operated tint meters, March 1, 2012, Office of the South Carolina Attorney General (https://www.scag.gov/wp-content/uploads/2012/03/wunderlich-r-h-os-9401-3-1-12-use-of-battery-operated-tint-meters.pdf), accessed October 2026
- Automotive Window Film and Your Car, International Window Film Association (https://iwfa.com/automotive/), accessed October 2026
- 49 CFR 571.205, Standard No. 205, Glazing materials, eCFR (https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.205), accessed October 2026
Prices on this page are The Auto Show’s published starting prices. Film ratings and warranty terms come from the manufacturer. This guide explains South Carolina law in plain words; it is not legal advice.