I have purchased some Mondial Damasco yarn, which is Italian yarn. 
The measurement listed on the packaging is  g50 = m50.  I need this
measurement coverted to feet or yards.  I cannot find a conversion
chart anywhere on your web site that will do the conversion.

I suspect that g50 = m50 means that the ball or skein of yarn has a
weight of 50 grams, and the yarn is 50 meters long, which is
approximately 164 feet.

Supporting pinkfreud's suspicion, I found sites that sell this stuff
and say a unit weighs 50 grams and is 55 yards long, which is 165
feet.

http://www.yarns-and.com/Mondial/MONdamasco.htm

http://www.discountyarnsale.com/pd_mondial_damasco.cfm

http://www.knittingfever.com/knitpatterns.asp?manu=Mondial&yarn=Damasco&prodid=4703&prodtype=yarn&detail=no

The above comments are not quite right but almost there. When you deal
with yarns, robes or anyting of similar nature the normal unit of
measure is linear density rather than length i.e. some expression of
weight per length. There are various systems still in common use. The
two most common are Denier and Tex. Denier is the old system still
used by the nylon industry i.e. pantyhose and is the weight in grams
of 9000m. hence 15 denier stockings are made from fibres having a
weight of 15grammes per 9000metres. Pretty fine. The more modern unit
is Tex whih again is grammes per 1 kilometre in this case i,e, 1000m.
So 50 Denier is about 5.5 Tex. You will also see decitex quoted which
is grammes per 10,000 metres. This is used when the Tex values get
really small.

Finally there is also the formal SI system of measuring linear density
which quotes metres per kilogramme of material and is designated by
the M number on your product. Hence M50 means the product is 50 metres
long for every kilogram of product. Or in your units that is about 164
feet per 2.2 pounds or 74.5 feet per pound. so just weight what you
have in pounds and multiply by the above figure.
Hope that helps. www.bayworth.com

Further information

You may find this link a helpful conversion. Go to linear density.

BS947 deals with this subject.  It gives the following:

Tex = grammes per kilometre
decitex = decigrammes per kilometre
kilotex = kilogrammes per kilometre

Denier = grammes pr 9000 metres

These units have some popularity as they could be used fairly directly
in calculating/expressing properties such as tenacity, breaking
length, etc.

They are described as Direct Systems, ie: mass per unit length.  The
Metric unit is Indirect and in BS947 is given units of
metres per kilogram

The above comment is interesting and illuminating, but not quite right.

First, in accordance with conventional notions of density, where
higher density means more mass per area or volume, the SI measure of
linear density is kilograms per meter, not meters per kilogram.

http://en.wikipedia.org/wiki/Linear_mass

http://standards.iso.org/ittf/PubliclyAvailableStandards/C030810E_FILES/MAIN_C030810E/text/unit_eq_J.html

http://www.oiml.org/publications/D/D002-e99.pdf

Second, a product of which 50 meters weighs one kilogram would be more
like rope than yarn.  50 meters per kilogram is 20 kilotex. 
Quarter-inch polypropylene rope has a density of 17.1 kilotex.

http://www.unols.org/publications/winch_wire_handbook__3rd_ed/12_useful_info.PDF

Heavyweight knitting yarn at 100 grams per 147 meters is only 680 tex.
 You can't measure density from a picture, but the Mondial Damasco
does not look 29 times denser than heavy knitting yarn.

http://www.sewknit.ca/patons_specification.htm

http://www.yarn.com/yarns-knitting/fiber_main.html

Note that in the retail yarn market, the units used in product
descriptions are weight and length, not density, and yarn is sold in
units of standardized weight and length, not cut to order.

Finally, considering that multiple websites selling the product list
units of 50 grams and 55 yards, which is very close to 50 meters, "g50
= m50" on the package seems much more likely to mean 50 meters length
than 50 meters per kilogram.

Here's one more, which actually lists the length as "±50m."

http://craft.yokolab.com/product/y_mondial.html