Free tool · no sign-up
Weld dilution calculator
Dilution is the share of the finished bead that came from the plate rather than from the wire. Enter the melted and deposited areas from a macro-section, or the penetration and reinforcement of the bead, and read the percentage — together with what that mixture does to the content of any element you care about.
It matters most where the surface is the product: an overlay, a cladding layer, a buttering pass, or a dissimilar joint whose chemistry has to land inside a band.
One ratio, two ways to measure it
Dilution D = Abase / (Abase + Afiller)
From the bead profile D = p / (p + h), taking both parts as parabolic segments over one bead width
Resulting composition Xweld = D · Xbase + (1 − D) · Xfiller
A = cross-sectional area · p = penetration below the original surface · h = reinforcement above it · X = content of one element in weight percent
The two routes are the same ratio measured differently. On a macro-section the areas are planimetered directly and the answer is defensible. From the bead profile the width appears in both areas and cancels, which is why penetration and reinforcement alone are enough — and also why the estimate degrades on any bead whose penetration is much narrower than its cap.
How to calculate weld dilution
Whichever evidence you have — an etched section or a bead you can measure.
- Choose the input basis. Measured areas if you have a macro-section; penetration and reinforcement if you are setting parameters at the machine.
- Measure below and above the original plate surface. The melted parent metal is everything below the line the plate surface used to occupy; the deposit is everything above it. Getting that datum wrong is the most common error in the whole calculation.
- Read the dilution percentage. The share of the fused metal that came from the plate. The complement is the share that came from the consumable.
- Add the two compositions to see the deposit. Enter the element content of the parent metal and of the consumable, and the tool returns what the mixed bead actually contains — the number a corrosion or hardness requirement is written against.
- Compare against the maximum the procedure allows. Type the limit your overlay or cladding specification imposes and the tool reports the margin in points.
- The datum is the original plate surface. Everything below it is melted parent metal, everything above it is deposit. On a grooved joint the previous pass is the datum for the next one, which is why layer two of an overlay dilutes far less than layer one.
- Composition is why anyone measures this. A 22 % chromium consumable laid at 40 % dilution does not give a 22 % chromium surface, and the second layer exists to fix exactly that. Enter both compositions above to see where the first layer actually lands.
- Parameters move it more than consumables do. Current, arc length, polarity, travel speed, torch angle and groove width all change how much plate is melted per unit of wire fed. The heat input calculator quantifies the energy side of that trade.
- Equal densities is an assumption, not a law. The mass balance holds for steel on steel. A nickel alloy on carbon steel, or an aluminium bronze overlay, needs the densities carried through explicitly.
- The section comes weeks after the weld. Watching the pool while it is molten is the only way to catch a penetration change on the pass that produced it — see PoolDrop and the overlay monitoring article.
For dilution control on cladding and overlay work, read weld overlay and cladding quality monitoring.
Questions engineers ask about this calculation
How is weld dilution calculated?
Dilution is the melted parent-metal area divided by the total fused area: D = A_base / (A_base + A_filler), taken from an etched macro-section of the bead and usually quoted as a percentage. Where no macro exists, the same ratio follows from the bead profile as D = p / (p + h), with p the penetration below the original surface and h the reinforcement above it — the bead width cancels because both parts are approximated as parabolic segments over the same width.
What does dilution do to the composition of the deposit?
It mixes the two metals, so the deposit is neither the plate nor the consumable. For any element the mass balance is X_weld = D × X_base + (1 − D) × X_filler, taking the two densities as effectively equal. That is why a corrosion-resistant overlay is specified by the chemistry of the finished surface rather than by the wire: at 40 % dilution a nominally 22 % chromium consumable lands well short of 22 % in the first layer, which is the usual reason a second layer is required.
Which welding parameters raise dilution?
Anything that puts more energy into melting the plate rather than the wire. Higher current, a shorter arc, DCEP polarity on solid wire, a slower travel speed relative to the wire feed, a leading torch angle and welding into a narrow groove all raise it. Lowering it means feeding more wire per unit of arc energy — weaving, a trailing angle, a higher wire feed at the same current, or a strip electrode instead of wire when the requirement is a low-dilution overlay.
When is the penetration-and-reinforcement estimate not good enough?
Whenever the bead has a finger of deep penetration under a much wider cap, which is normal in spray-transfer GMAW and in submerged arc. The two-parabola approximation assumes the melted and the deposited parts share a single width, and a narrow finger breaks that assumption in the direction that makes the estimate read low. It is a useful figure while setting parameters; it is not a figure to put in a procedure qualification record, where the macro-section is what the standard asks for anyway.
Dilution is set by the arc, and the arc is not on the drawing.
PoolDrop watches the weld pool at 480 fps and HeatCore AI scores the thermal signature of every pass, so a penetration that crept up when the current drifted shows as a change in the pool rather than as a chemistry result from a laboratory three weeks later.
