🚗

Window Tint Calculator

Find the real VLT of a tinted car window: factory glass × film (or two films) gives the combined visible light transmission, checked against your legal limit, with the darkest film you can legally add.

Factory glass VLT

Tint film

Second film layer

Legal minimum VLT for this window

Loading calculator…

How it works

combined VLT = glass VLT × film VLT (× second film VLT), as fractions · darkest legal film = limit ÷ glass VLT

Visible light transmission (VLT) is the share of visible light a window lets through. Layers multiply rather than subtract: a 35% film on glass that already passes 80% leaves 0.80 × 0.35 = 28%, not 35%. Police meters measure that combined figure, so a film that looks legal on paper can fail on tinted factory glass. Limits differ widely — 70% for front side windows in the EU and many US states, 35% or less elsewhere, and usually no limit behind the driver — so check your own country or state rules and allow a few points for meter tolerance.

Worked example

A 35% film on 80% factory glass gives 80% × 35% = 28.0% combined VLT, which is too dark for a 70% front-window limit; on that glass the darkest legal film would be 70 ÷ 0.80 = 87.5% VLT — in practice a clear heat-rejection film.

Sources: International Window Film Association (IWFA) · UN ECE Regulation No. 43 — Safety glazing

Frequently asked questions

How do I calculate the VLT of tint on factory glass?

Multiply the two percentages as decimals: 0.75 glass × 0.20 film = 0.15, so 15% VLT. Each extra layer multiplies again.

What does 35% tint mean?

The film alone lets through 35% of visible light. On a real window the result is lower — typically 26–30% — because the glass itself blocks some light.

Is 5% limo tint legal?

Rarely on front windows; many places allow it only on rear side and back windows of passenger vehicles, and some ban it entirely. Check local law, including medical exemptions.

Does darker tint block more heat?

Not necessarily. Heat rejection depends on infrared-blocking technology (ceramic, spectrally selective films); a light 70% ceramic film can reject more heat than a cheap dark dyed film.

Related calculators

Car Paint Quantity Calculator

Estimate how much automotive paint a respray needs: basecoat and clearcoat (or single stage) from the body area, number of coats, coverage and spray-gun transfer efficiency, with the reducer or activator for the mixing ratio and the amount to buy in quarts, gallons or litres.

Vinyl Wrap Material Calculator

Work out how many linear feet and square feet of vinyl a full or partial vehicle wrap needs, including a waste allowance for overlaps and mistakes.

Window Solar Heat Gain Calculator

Solar heat entering through a window from its area, orientation, SHGC and shading — peak watts and BTU/h, the cooling load it adds in tons, daily energy on a sunny day, and how much low-SHGC glass, overhangs or exterior shades would cut it.

This calculator is for educational purposes. Double-check important results before acting on them.