# Imperial to Metric Conversion Error Prevention Checklist > Source: https://netray.co/tools/imperial-metric-conversion-error-prevention-checklist > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer A 30-point checklist for catching unit mix-ups between drawings, suppliers, ERP data, programs and inspection. ## Category quality ## Audience - Quality engineer - Design engineer - Buyer - ERP administrator - CNC programmer ## Tool **Kind:** checklist **Groups:** #### Drawings and specifications **Items:** **Text:** Drawing states its primary unit system in the title block or general notes **Critical:** true **Text:** Tolerances are stated in the same unit as the dimension they apply to **Critical:** true **Text:** Any dual dimensions show which unit governs **Critical:** true Converted dimensions keep full precision until final rounding Material thickness is given as a value, not only as a gauge number Thread callouts name the series and standard (UNC, UNF, metric coarse or fine) Customer drawings in another unit system are not silently redrawn without approval #### Purchasing and suppliers **Items:** **Text:** Purchase orders state units on every dimensional and quantity line **Critical:** true Bar, tube and plate stock sizes are checked for nominal versus actual size Supplier certificates report values in the units the specification requires **Text:** Pack sizes and unit prices use the same UoM as the receiving unit **Critical:** true Fasteners are ordered with standard and property class or grade, not size alone Substituting an inch part for a metric part goes through engineering approval #### ERP and item master **Items:** **Text:** Every item has stock, purchase and sales UoM that are intentional **Critical:** true **Text:** Conversion factors are checked in both directions for reciprocity **Critical:** true Weight and dimension fields state a unit and use it consistently Item descriptions carry the size in one agreed unit format Decimal places per UoM suit the item (whole each, fractional kilograms) Unit costs are verified after any UoM or conversion change Open purchase orders and inventory are reviewed before changing a factor #### Shop floor and CNC **Items:** **Text:** Programs declare the unit mode (G20 inch or G21 metric) at the start **Critical:** true **Text:** Tool tables and offsets are in the unit mode the program expects **Critical:** true Operators check unit mode on the control before running a first piece Feed rates are expressed per minute or per revolution as intended Setup sheets list the unit system for each dimension Fixtures and gauges are labelled with their nominal unit #### Inspection and records **Items:** **Text:** Inspection plans list characteristics in the drawing unit system **Critical:** true Gauges and calibration records show units and resolution Measurements are taken at the standard reference temperature where it matters Inspection reports show the unit with every value **Text:** Torque specs state the unit (N.m, lbf.ft, lbf.in) and lubrication condition **Critical:** true Conversion factors used are documented, not remembered **Scoring Note:** Count ticked items over total items per group. Any group below 85 percent deserves a corrective action. Any critical item not ticked is a likely route for a unit mix-up reaching the customer, so fix those first and record the owner and due date. ## Content **Intro:** Unit mix-ups are a classic quality escape: an inch value read as millimetres, a program run in the wrong mode, a torque quoted in the wrong unit. This checklist walks through drawings, purchasing, ERP data, CNC and inspection to close the common gaps. **Sections:** #### How to use the checklist **Body:** Run it as a review for a new part, a new supplier or a drawing that moves between inch and metric plants. Tick what is true and note owners for the rest. The groups follow the life of a dimension from the drawing to the PO, the item record, the machine and the inspection report. Export the result to PDF or Excel and attach it to the first article or the supplier approval file. A short version covering only the critical items works well as an audit sample. #### Why these controls **Body:** Unit errors are rarely arithmetic errors. They happen at hand-offs, where a value loses its unit label or an assumption of a default unit crosses a boundary. Each group targets one hand-off: engineering to buyer, buyer to supplier, supplier to ERP, ERP to shop and shop to quality. Requiring that every number travels with its unit and its standard is the cheapest and most effective control, and it costs nothing in tooling. **Bullets:** - State the unit with every number - Convert once, at full precision, and document the factor - Make machines declare unit mode explicitly - Check conversions in both directions #### Common failure patterns **Body:** Frequent causes include a drawing revised in one unit system while the supplier works from an older copy in the other, rounding a converted tolerance so that the part band shrinks or widens, and ERP descriptions that mix 1/2 inch and 12.7 mm for the same item. Another is relying on operator memory for the right torque unit. Consider a periodic duplicate scan in the item master to find the same part held under both unit descriptions. **Cta:** If you want unit consistency checked automatically across your ERP item data, purchase orders and inspection records, we can help build read-only checks on your own data. **Faq:** #### What is the most common cause of inch and metric mix-ups? **Answer:** Missing or implied units at a hand-off. A dimension without a unit label, a program without an explicit mode, or a PO line that omits the unit lets each person assume their default. #### Should I convert tolerances like dimensions? **Answer:** Convert both at full precision, then round the limits so the resulting band is not larger than the original. Rounding tolerances toward the tighter side is safer, and the choice should be written into the drawing note. #### Which G-codes control CNC units? **Answer:** On most Fanuc-style controls G20 selects inch mode and G21 selects metric mode. Put the code at the start of the program, and confirm tool offsets and work offsets are set in the same mode. #### How often should this checklist be used? **Answer:** Use it on new parts, new suppliers, drawing transfers between plants and after any ERP UoM change. For stable parts, a yearly sample audit of the critical items is usually enough. ## Search terms unit conversion error prevention, imperial metric mix up checklist, metric inch conversion quality checklist, drawing units checklist, unit of measure control manufacturing, metric conversion drawing review, uom error prevention erp, dual dimensioning checklist --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json