Window Tint Calculator
Enter the glass VLT and the film VLT and get the combined light transmission, compare it with your state's limit, and find the darkest film that stays legal on your glass.
Factory glass without film. Factory glass is often slightly tinted; a tint meter gives the real figure.
E.g. 35, or 50, 70 for film over existing film.
VLT = visible light transmission, the share of light that gets through. The result updates as you type.
Net VLT (glass + film)
26.2% of light gets through
73.8% blocked
| Calculation | 75% × 35% = 26.25% |
| Film | Net VLT on this glass |
|---|---|
| 5% | 3.8% |
| 15% | 11.3% |
| 20% | 15% |
| 35% | 26.3% |
| 50% | 37.5% |
| 70% | 52.5% |
| 80% | 60% |
What this page cannot tell you
What your state's law says, or what a meter will read. States differ on limits for each window, whether they count film alone or film plus glass, reflectivity rules and the tolerance they allow; check your state's vehicle code. Multiplying ignores light that bounces between layers, so a meter can read a point or two differently.
How to calculate net window tint VLT
- Enter the glass VLT. The light transmission of the glass without film — a tint meter reading is best.
- Enter the film VLT. From the film's box, e.g. 35%. For film over existing film, list both.
- Add your state's minimum. Optional: the legal minimum for that window.
- Read the net VLT. And the darkest film that keeps that glass at the limit.
10 situations where a window tint calculator helps
Choosing a film shade
A '35%' film on factory glass ends up darker than 35%; see the real number.
Staying within your state's limit
Find the darkest film that keeps the combined figure legal on your glass.
Cars with factory privacy glass
Rear glass is often already tinted; add film and see the result.
Layering film over old film
Enter both layers to see how dark it gets.
Tint shops quoting customers
Show the net figure before the install.
After a ticket
Understand why a meter read lower than the film's label.
Home and office windows
The same multiplication applies to residential film on glass.
Comparing films side by side
The table shows several common film shades on your glass.
Buying a used car with tint
Estimate what film was used from a meter reading.
Night visibility decisions
See how much light actually gets through.
How net VLT is worked out
VLT (visible light transmission) is the share of visible light a layer lets through. Light that passes the glass and then the film keeps the fraction each one transmits, so the combined figure is the product: a 35% film on 75% glass gives 0.35 × 0.75 = 26.25%. That's why the meter reading is darker than the film's label.
The combined figure is what matters in most places. The film maker Madico notes that 'the majority of states measure the VLT in terms of the combined light transmittance of both the film and the glass itself.'
Limits: the product ignores light that bounces between the layers, so a meter can read a point or two different, and meters themselves have tolerances. Laws differ by state and by window — front sides, rear sides, back glass and the windshield strip — and some states also regulate reflectivity or colour. This page doesn't hold any state's law; check your state's vehicle code. Everything runs in your browser.
Sources
- Madico — Car window tinting laws: what you need to know — Most states measure the combined film-and-glass VLT
Frequently asked questions
How do I calculate net VLT?
Multiply the glass VLT by the film VLT as fractions. 70% glass with 35% film is 0.70 × 0.35 = 24.5%.
Why does my 35% tint read darker on a meter?
Because the glass itself blocks some light; the meter reads the combination.
What tint percentage is legal?
It depends on your state and the window. Enter your state's figure as the limit to check.
What is VLT?
Visible light transmission — the percentage of visible light that passes through. Lower means darker.
Can I put film over existing tint?
The page will show the combined figure if you list both layers; whether it's allowed is up to your state's law.
Does this apply to house windows?
Yes, the arithmetic is the same for any film on glass.
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