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Unit of Measure Conversion Reference for ERP

Wrong unit of measure conversions quietly corrupt purchasing, inventory value and costing. This reference lists common conversion factors, flags which are exact by definition, and explains how to hold them in an ERP item master without rounding errors.

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From	To	Multiply by	Dimension	Note
in	mm	25.4	Length	Exact by definition
ft	m	0.3048	Length	Exact by definition
yd	m	0.9144	Length	Exact by definition
mile	km	1.609344	Length	Exact by definition
mil (thou)	mm	0.0254	Length	1 mil = 0.001 in
ft	in	12	Length	Exact
m	mm	1000	Length	Exact
cm	mm	10	Length	Exact
lb	kg	0.45359237	Mass	Exact by definition (avoirdupois)
oz	g	28.349523125	Mass	Avoirdupois ounce, exact
lb	oz	16	Mass	Exact
kg	g	1000	Mass	Exact
metric ton (t)	kg	1000	Mass	Exact
short ton (US)	kg	907.18474	Mass	2,000 lb
long ton (UK)	kg	1016.0469088	Mass	2,240 lb
troy oz	g	31.1034768	Mass	Precious metals
L	mL	1000	Volume	Exact
m3	L	1000	Volume	Exact
gal (US)	L	3.785411784	Volume	Exact by definition
gal (imperial)	L	4.54609	Volume	Exact by definition
qt (US)	L	0.946352946	Volume	1/4 US gallon
gal (US)	qt (US)	4	Volume	Exact
fl oz (US)	mL	29.5735295625	Volume	1/128 US gallon
ft3	L	28.316846592	Volume	Exact from ft definition
barrel (oil)	L	158.987294928	Volume	42 US gallons
in2	mm2	645.16	Area	Exact
ft2	m2	0.09290304	Area	Exact
yd2	m2	0.83612736	Area	Exact
m2	ft2	10.7639104167	Area	Inverse of 0.09290304
bar	kPa	100	Pressure	Exact
psi	kPa	6.894757293	Pressure	Approximate to 9 digits
MPa	kPa	1000	Pressure	Exact
h	min	60	Time	Exact
min	s	60	Time	Exact
day	h	24	Time	Exact
dozen (DZ)	each (EA)	12	Count	Exact
gross (GR)	each (EA)	144	Count	12 dozen
gross (GR)	dozen (DZ)	12	Count	Exact
pair (PR)	each (EA)	2	Count	Exact
ream	sheet	500	Count	Common paper definition

Multiply the quantity in the From unit by the factor to get the To unit. To go the other way, divide. Conversion factors in your ERP should keep enough decimals; rounding a factor like 0.45359237 to 0.454 causes visible drift on large quantities. Pack sizes (case, pallet, reel) are item specific and are not listed here.

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How to use the table

Search by unit name or dimension, then multiply the quantity in the From unit by the factor to get the To unit. Divide to go the opposite direction. Use the table when you set up base and alternate UoMs on an item, when you check a supplier price unit against your stock unit, or when you review conversion records during a data migration. Export to Excel or CSV for use in a load template.

Exact versus approximate factors

Many factors are exact since the inch, pound and gallon are defined in terms of metric units: 1 inch is exactly 25.4 mm, and 1 pound is exactly 0.45359237 kg. Others, such as psi to kPa, are derived and rounded. Keep as many digits as the ERP field allows. If a system limits decimals, prefer a numerator and denominator pair, if supported, over a rounded single factor.

Exact: in, ft, yd, mile, lb, US gallon
Derived: psi to kPa, barrel to liter
Count units: dozen and gross are exact
Pack sizes are item specific, never generic

UoM setup in an ERP

Most ERPs keep one base unit per item and alternate units with a conversion factor. Choose the base unit as the smallest unit you track in stock, so quantities stay whole where possible. Purchase and sales units then convert into it. SAP material master holds alternative units of measure with a numerator and denominator, and many other systems store a single decimal factor. Check how yours treats rounding on receipt and invoice, since small differences multiply across thousands of transactions.

Common mistakes

Mixing US and imperial gallons or short and long tons is the classic error and it is silent. Entering the factor in the wrong direction multiplies instead of dividing. Rounding factors to three decimals causes cost and quantity drift. Allowing free-text units creates duplicates like EA, EACH and PC. Changing the base unit of an item with stock or open orders is dangerous and should be done only through the ERP's supported process, if at all.

Frequently Asked Questions

What base unit of measure should I choose for an item?

Use the smallest unit you need to track in stock so that quantities stay whole where practical, for example each or gram. Larger purchase and sales units then convert into it. Avoid changing it later once stock and transactions exist.

Are US and imperial gallons the same?

No. A US gallon is exactly 3.785411784 liters and an imperial gallon is exactly 4.54609 liters, about 20 percent larger. Confirm which one a supplier uses before setting a conversion.

How many decimals should a conversion factor have?

Keep as many as your ERP allows, at least six for derived factors. Exact factors such as 25.4 or 0.45359237 should be stored in full. Where possible use a numerator and denominator to avoid rounding altogether.

Does this table include pack sizes like case or pallet?

No. Case, box, reel and pallet quantities depend on the item and the supplier, so they must be entered per item from the packaging specification, not from a generic table.

If you are cleaning UoM data across thousands of items, we can help build a read-only scan that flags inconsistent or implausible conversions in your ERP.

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