Brass reference / Tools
Weighted Average Lead Content Calculator
NSF/ANSI 372 limits the wetted surfaces of a potable water assembly to a 0.25 percent weighted average lead content. This works out where your assembly lands.
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Your wetted components
Add each component whose surface touches the water. Enter its wetted surface area and its lead content, or pick an alloy to fill the lead figure in.
| Component | Alloy preset | Wetted area | Lead % | Share |
|---|
How the number is worked out
The arithmetic is short, and getting it wrong usually means treating 0.25 percent as a limit on every alloy rather than on the assembly.
weighted average =
sum( area_i x lead_i ) / sum( area_i )
for every wetted component iEach component is weighted by its share of the total wetted surface area. A small leaded component inside a large compliant body can still pass. A single machined fitting usually cannot, because one alloy is nearly all of the wetted area.
What this does not tell you
Three limits worth being clear about, because the calculation is the easy half of the problem.
- Not NSF/ANSI 61That is a health effects standard covering what the material leaches, and it requires testing rather than a composition calculation. Many parts need both.
- Not certificationCertification is granted by an accredited body to a named product from a named manufacturer at a named facility. No calculator and no machine shop can hand you that.
- Not your lotThe presets are published nominal values for the alloy. Your mill certificate gives the figure for the material you actually received, and that is the number for a real submission.
This tool is a design aid, not a compliance determination, and it is not legal advice. Background is in NSF/ANSI 61 and 372 for brass fittings.
Questions about the calculation
Is 0.25 percent a limit on each alloy, or on the whole assembly?
On the whole assembly. NSF/ANSI 372 sets a weighted average across the wetted surfaces of a pipe, fitting or fixture. Each wetted component is weighted by its share of the total wetted surface area, and the weighted result must not exceed 0.25 percent. A single component above 0.25 percent does not automatically fail the assembly, though on a small machined fitting one alloy is usually almost all of the wetted area.
What surface area do I use?
Only the wetted surface, meaning the surface in contact with water in normal use. External surfaces, threads outside the wetted path and dry faces are excluded. Bore surfaces, seat faces and any internal passage the water passes through are included.
Does this cover solder and flux?
No. Solder and flux carry a separate limit of 0.2 percent under the same law and are not part of the weighted average calculation for the wetted components. If your assembly is soldered, that is a separate check.
Does passing this calculation make my part compliant?
No. It tells you whether the lead content arithmetic works. NSF/ANSI 61 is a separate health effects standard that requires testing rather than a composition calculation, and certification is granted by an accredited body to a specific product from a specific manufacturer. This tool is a design aid, not a compliance determination, and it is not legal advice.
Where do the preset lead percentages come from?
They are midpoints or upper bounds of the published nominal composition range for each alloy, taken from the alloy datasheets on this site. Your actual material certificate will give a specific figure for your lot, and that is the number to use for a real submission.
Need a shop that runs lead-free brass?
Send the drawing and set the compliance field. We only match potable water parts to shops that already run lead-free grades and supply certificates.