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.
| 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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