A:B describes the relation between components, not necessarily their percentages of the total. Correct arithmetic is only one part of an approved product procedure.
1. Copy the applicable specification
Record the exact product and compatible A/B components, document revision and ratio basis. A mass ratio is not interchangeable with a volume ratio: different component densities can make the numbers differ. If only a volume ratio is available, do not put it into the mass-ratio calculator. Obtain the maker’s mass instructions instead.
Smooth-On — mass and volume ratios differ; product-specific instructions (English) ↗2. Define what the scale must measure
The calculator input M is combined net material mass, without the container. A fictional 350 g empty container plus 600 g material is 950 g gross load. Tare changes the display, not physical capacity. Check the scale’s useful increment and specified performance for the smaller component, not just the total. A stable display alone does not prove accuracy.
3. Verify the denominator before dosing
For a fictional A:B = 100:20 and M = 600 g, A = 600 × 100 / 120 = 500 g and B = 600 × 20 / 120 = 100 g. B is 20 parts per 100 parts of A, but 100 / 600 = 16.67% of the total. Using 20% of 600 g would give 480 g + 120 g, a different ratio of 4:1 instead of 5:1.
Record the separate net amounts and their sum. If A was already dispensed as 600 g, B would be 120 g and combined M 720 g, not 600 g. These are arithmetic examples, not recommended product ratios, tolerances or batch sizes.
4. Keep product decisions outside the arithmetic
Use the product instructions and safety data for permitted quantities, container, handling, mixing and working time. Reactive materials can generate heat; maintaining a ratio does not prove that scaling up is safe. Do not alter a specified ratio to change curing time or use this result for food, medical use or a safety-critical repair. If basis, components or required measuring performance are unclear, stop and ask the supplier.
WEST SYSTEM — dispensing, ratio and heat limitations; epoxy-specific (English) ↗Keep this record with the batch
| Record | Retain | Why it matters |
|---|---|---|
| Specification | Product, A/B identity, revision, mass basis | Prevents borrowing a ratio from another system |
| Weighing | Scale ID, check status, tare, unit, net A and B | Distinguishes the container from material |
| Conditions | Time, temperature and permitted batch size from instructions | Arithmetic does not set handling conditions |
| Outcome | Actual quantities and anomalies, not just calculated targets | Targets do not prove what was dispensed |
Worked example
A target and a wrong-denominator comparison
Fictional target: combined net 600 g at mass ratio 100:20.
A = 600 × 100 / 120 = 500 g B = 600 × 20 / 120 = 100 g A + B = 600 g; B / (A + B) = 16.67% 480 / 120 = 4; 500 / 100 = 5
20 parts per 100 of A is not 20% of combined mass. Keep the product’s ratio and verify that the scale can measure each required quantity.
What to have ready
- Exact compatible components and current specification
- Confirmed mass ratio, not volume ratio
- Combined net target separated from tare and component A alone
- Scale capacity and useful small-mass performance checked
- Product’s permitted batch and handling limits retained
Common mistakes
- Treating 100:20 as 80% A + 20% B.
- Entering only A’s mass as the combined target.
- Using extra hardener to change working time.
- Assuming a correct ratio certifies cure, strength or safe batch size.
Tools for these measurements
Prepare the measurements with these instrument guides.
Use and limitations. Sources include US public agencies. Principles are general; regulations and design values must be checked where you live.Worked examples use stated hypothetical inputs.