Walk into any tint shop and the first question you will be asked is how dark you want to go. It sounds simple until you are standing in front of a sample board full of numbers that seem to mean the opposite of what they say. The window tint percentage you choose affects how your car looks, how well you see at night, whether you pass a traffic stop without a ticket, and how the cabin feels in a St. Louis July. It deserves more thought than pointing at the darkest square.

This guide covers what the percentages actually measure, what Missouri allows on each window, and the combinations we install most often at our tint shops around St. Louis.

How Tint Percentages Actually Work

The number on a tint sample is VLT — Visible Light Transmission. It measures how much visible light passes through the film. A 70% film lets 70% of light through and looks nearly clear. A 5% film lets 5% through and reads as limo black. The scale runs backward from how most people expect: lower number, darker window.

Film stacks on top of your glass

Your windows are not perfectly clear to begin with. Most automotive glass transmits roughly 75–80% of light on its own. Film multiplies against that, so a 35% film on 78% glass lands around 27% combined. This is why two cars with “35% tint” can look slightly different shades, and why a shop that measures your actual glass before recommending a film is doing you a favor.

The percentage is not the whole product

Two films with identical VLT can perform completely differently on heat, because darkness and heat rejection are separate specifications. We broke that down fully in our ceramic vs. carbon vs. dyed film comparison — worth reading before you fixate on a shade.

What Missouri Law Allows

Missouri regulates each zone of the vehicle differently, and the front side windows are the ones that get drivers pulled over:

• Windshield: non-reflective tint above the AS-1 line only. Full-windshield films must stay in the near-clear range.
• Front side windows: must allow at least 35% of light through. This is the number enforcement checks with a meter.
• Rear side windows and back glass: may be darker on most passenger vehicles, provided the vehicle has working side mirrors.

There are nuances — measurement tolerance, medical permits, how the rules apply to SUVs versus sedans — and we covered them in detail in our Missouri window tint law guide. The short version: plan on 35% or lighter for the front doors and you have real freedom everywhere behind the driver.

The Common Percentages, Side by Side

These four shades cover nearly every install we do:

50% is the sleeper option. On a quality ceramic film it knocks down heat and glare dramatically while looking close to stock — a favorite for drivers who want comfort without changing the car’s appearance, and the only sensible range for windshield film.

35% is the default for a reason: visibly tinted, still easy to see out of at night, and legal on every window of a Missouri passenger car. If you want one number all the way around, this is it.

20% reads as dark from outside but remains workable from the driver’s seat in daylight. It is the closest match to most factory privacy glass, which makes it the go-to for tinting front doors behind the legal line — meaning on the rear half — so the whole vehicle looks uniform.

5% is a statement. From outside you see nothing; at night, from inside, you see very little. We install plenty of it on back glass and on show builds, but we talk customers out of it more often than into it.

Matching a Percentage to Each Window

The best setups treat the car as zones rather than picking one number.

Windshield

A near-clear ceramic film (70–80% VLT) on the windshield blocks a large share of infrared heat and UV without darkening your view. In a region with summers like ours, it is the single most comfort-per-dollar piece of film on the car.

Front side windows

35% is the ceiling for darkness in Missouri, and it happens to be a sweet spot: enough shade to cut glare and match the rear, light enough for safe night driving and clear eye contact at four-way stops.

Rear doors and back glass

If your vehicle came with factory privacy glass — like the Escalade pictured above — understand that the factory tint is dyed into the glass and blocks almost no heat. Adding a light ceramic film over it keeps the same look while finally making the back seat comfortable, which matters if you haul kids in car seats. On vehicles without privacy glass, 20% in the rear paired with 35% fronts is the most requested combination we do.

Darkness Is Not Heat Rejection

The most expensive mistake in tint shopping is assuming the darkest film is the coolest. Heat performance is measured by TSER (total solar energy rejected), and it is driven by what the film is made of, not how dark it is. A 50% ceramic film can reject more total heat than a 20% dyed film, because ceramic particles block infrared energy that darkness alone does not touch.

UV protection, for what it is worth, is the one spec that does not vary much: virtually any quality film blocks 99% of UV at any shade, which protects both your skin and your interior from fading.

What St. Louis Drivers Usually Choose

Daily commuter, sedan: 35% all around. Legal, uniform, easy to live with year-round on I-64 sun-glare mornings.

Family SUV or truck with privacy glass: 35% on the front doors to match the factory rear, plus a clear ceramic windshield film. The vehicle looks finished and the cabin cools down noticeably faster.

Privacy-focused: 35% fronts, 20% rears. Dark enough that cargo and kids are not on display in a parking lot, without the night-driving penalty of 5%.

Show or weekend car: whatever the build calls for — but keep the fronts legal. A ticket and a forced peel-off is a bad ending for a good install.

Every shade in this article is on the sample boards at all three of our shops — South County, West County in Ellisville, and Chesterfield — and looking through a sample beats guessing from photos every time.

Mistakes to Avoid

• Going darkest on the first car. You cannot lighten film without a full removal. Start at 35% or 20%; you can always go darker on the next install.
• Copying a car from another state. That 20% front-door setup you saw on social media may be legal where it was filmed. It is not legal here.
• Ignoring night driving. Rain at night on an unlit stretch of Highway 109 through 5% film is a genuinely bad experience. Think about your worst-case drive, not the showroom lighting.
• Judging the shade the day of install. Film looks hazier and slightly lighter while it cures. Give it time before you decide it is wrong — our cure time guide explains what to expect week by week.

Frequently Asked Questions