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GSM to Microns. Converting galvanizing weight to thickness

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User's Guide to Hot Dip Galvanizing for Corrosion Protection in Atmospheric Service
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A. The density of zinc is 7.4 7.14 g/cm^3; there are 10^4 µm in a cm, so there are 10^12 µm^3 in a cm^3. Therefore 1 µm/m^2 is equivalent to 7.4 7.14 X 10^-4 g of zinc.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

A. Trevor, the danger in this type of calculations is that one gets confused about all the different dimensions. The calculation I use is (using dimensions that are commonly used in the world of coatings): Weight of coating/mtr2 [grams/m2] = Film thickness [µ] x specific weight [grams/cm3].

In the case of Zn: specific weight is 7,4 7,14 grams/cm3: Zn weight/sqm = 7,4 7,14 grams/µ

Calculation is applicable with any coating, p.e. powder:

How much powder is on a part of 3 m2 with an average DFT of 80 µ and a specific weight of powder of 1.3 kg/dm3? Answer: 80 x 1.3 x 3 = 312 grams.

Remmelt Bosklopper
Remmelt Bosklopper
- Enschede, The Netherlands

A. I can Simplify the calculation method for converting gr/m2 to micron or micrometer.

D(density) = Wt. (weight)/ V (volume)
for Zinc
D = 7.4 7.14 g/cm3
= 7.4 7.14/cm*cm*cm.
1 cm = 10000 micron or micrometer.
= 7.4 7.14/cm*cm*10^4 µ.
10^4 µ = 7.4 7.14 g/cm*cm.
1 m = 100 cm.
10^4 µ = 7.4 7.14 g*100*100/(100*cm)*(100*cm).
10^4 µ = 7.4 7.14 g* 10^4/m*m.
1 µ = 7.4 7.14 g/m2 for one face.
1 µ = 14.8 14.28 g/m2 for two face.

for galvanization layer
25 µ = 185 178.5 g/m2 for one face
and 25 µ = 370 357g/m2 for two faces.

Nagy Emara
Kandil Steel - 10th of Ramadan - Egypt
August 25, 2014

Q. Many of my customers are asking that you says it's 90 GSM, but can you tell us in microns, and at this time I can't answer, so please let me know how to calculate micron to GSM and vice versa

R.Ashok Gour
- CHENNAI, Tamil Nadu, India
May 2, 2019

Defelsko Positector combo magnetic & eddy-current coating thickness tester

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A. Hi Ashok. They can measure the thickness of the galvanizing with a magnetic thickness meter if they wish confirmation.

Remelt has told us that 1 micron is about 7.4 7.14 GSM; so 90 GSM would apparently be somewhere around 12 microns. However, as Nagy implies, it is conventional that 90 GSM refers to the total amount of zinc applied to both sides of the strip, so I would expect the thickness to be about 6 microns per side.

You are welcome to refer them to this page where the question has been answered. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Most sources give the density of pure zinc as 7.14 g/cc. It will be slightly higher for Prime Western Zinc which is a zinc-lead alloy (up to 1.4% lead) but not much. The vast majority of hot dip galvanizing, until recently, was done with Prime Western Zinc. Other alloying components (aluminum, nickel, etc.) will have calculable effects on the density of the coating.

Tom Rochester
CTO - Jackson, Michigan, USA
Plating Systems & Technologies, Inc.
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"Handbook of Hot Dip Galvanization"
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thumbs up sign  Thanks for the more refined answer, Tom. 90 GSM then equals about 12,6 microns.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Q. In this calculation, what is 7.4?

Omprakash Sharma
Employee - Ghaziabad, UP , india
May 23, 2023

A. Hi Omprakash,
"7.4" was intended to be the density of zinc in grams per cubic centimeter, but that was a typo that was accidentally propagated across the whole page :-(
Then Tom advised us that it should actually be "7.14" :-)
After your inquiry we went back and corrected it throughout the page.
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

thumbs up sign Thanks for the corrections.
Omprakash Sharma [returning]
Employee - Ghaziabad, UP, india

A. ISO 1461 [affil link] standard states the thickness of zinc on steel in both formats, and says 85µ is 610 g/m2

Geoff Crowley
Crithwood Ltd.
supporting advertiser
Bathgate, Scotland, UK
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June 5, 2023

Ed. note: Thanks Geoff; that comes out to 7.18, pretty close to the 7.14 conversion factor above.


Q. If I have paper that is 32GSM what would be the approx. micron thickness.

Anthony Cuschieri
International Packaging Films (PET Film)s - Norwood, New Jersey USA
July 24, 2019

A. Hi Anthony. I don't know much about paper (this page is about galvanizing and the site's main focus is metal finishing), but a roll of coated magazine paper weighs far more than an equal size roll of toilet paper or even office paper. So I think your question isn't answerable because the density of different papers can apparently vary by 4:1 and probably more.


Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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