Calculation methodology

General rules

• Calculations run in the browser. Entered values are kept only in the page address, so the result survives a refresh and can be shared as a link.
• Decimal separator: comma in the Polish version, point in the English version. Fields accept both.
• A result appears only when the required data are complete – the missing fields are listed instead. The calculator never shows 0 in place of a missing value.
• Calculations use unrounded values; rounding (half up) applies to display only.
• In the chemical composition tools, elements not entered (other than the required ones) are taken as 0% and listed in a notice below the result.
• weldtools.pl is an independent, non-commercial website. It is not affiliated with IIW, EWF, ISO or any gas manufacturer. The site uses no cookies or analytics.

Arc energy and heat input

Arc energy E and heat input Q from welding current, arc voltage and travel speed.

Formulas

E = U · I / v · 10⁻³  [kJ/mm], v in mm/s

Q = k · E

1 kJ/mm = 10 kJ/cm

Calculation rules

• Thermal efficiency factor k per ISO/TR 17671-1 (EN 1011-1): MMA (111) 0.8 · SAW (121) 1.0 · MIG/MAG (131, 135, 136, 138) 0.8 · TIG (141) 0.6.
• Speed: mm/min ÷ 60, m/min × 1000 ÷ 60 → mm/s. Changing the unit does not convert the entered number.
• Min–max range: minimum from I min, U min and v max; maximum from I max, U max and v min; mean = (min + max) / 2.
• ±25% band (× 0.75 / 1.25): heat input range of qualification per ISO 15614-1 (level 2 – upper limit where impact requirements apply, lower limit where hardness requirements apply).
• ±15% band (× 0.85 / 1.15): permitted deviation for aluminium alloys of group 23 per ISO/TR 15608 (precipitation-hardenable alloys) according to EN ISO 15614-2:2025.
• Tolerance check: deviation = (Q − Q₀) / Q₀ · 100%; ±15% and ±25% limits inclusive. Check detailed requirements in the standard for your material and in the WPQR.

Rounding

kJ/mm – 3 decimal places, kJ/cm – 2 decimal places, deviation in % – 1 decimal place.

Carbon equivalents

Carbon equivalents CE, PCM, CET and CEN from the steel chemical composition in wt%.

Formulas

CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

PCM = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B

CET = C + (Mn + Mo)/10 + (Cr + Cu)/20 + Ni/40

CEN = C + A(C) · [Si/24 + Mn/6 + Cu/15 + Ni/20 + (Cr + Mo + Nb + V)/5 + 5B]

A(C) = 0.75 + 0.25 · tanh[20 · (C − 0.12)]

Calculation rules

• Weldability rating by CE (indicative scale – not defined by a standard; preheat is determined e.g. per EN 1011-2): ≤ 0.35 excellent · ≤ 0.40 very good · ≤ 0.45 good · ≤ 0.50 moderate · above 0.50 poor.
• Carbon content C is required. Other elements left empty are taken as 0% – the calculator lists which elements were not entered.
• Min–max range: CE for the minimum and maximum composition, the difference Δ and the weldability rating for both limits.
• CEN is calculated with the Yurioka formula including the A(C) function.

Rounding

3 decimal places.

Schaeffler diagram

Chromium and nickel equivalents and the position of the composition on a simplified Schaeffler diagram.

Formulas

Cr_eq = Cr + Mo + 1.5 · Si + 0.5 · Nb

Ni_eq = Ni + 30 · C + 0.5 · Mn

Calculation rules

• Cr and Ni contents are required. Other elements left empty are taken as 0% (with a notice).
• Simplified diagram: four boundary lines divide the field Cr_eq 0–40%, Ni_eq 0–30% into seven regions: A, A + M, M, A + F, A + F + M, F + M, F.
• The result shows the region where the point lies. It does not give the ferrite content (%) or ferrite number and does not account for nitrogen or cooling conditions; treat points close to boundary lines as indicative.
• Points outside the diagram are drawn on its edge.

Rounding

2 decimal places.

PREN – pitting resistance

Pitting resistance equivalent number of stainless steels from the chemical composition in wt%.

Formulas

PREN = Cr + 3.3 · (Mo + 0.5 · W) + 16 · N

Calculation rules

• Cr content is required. Mo, W and N left empty are taken as 0% (with a notice).
• Contributions: Cr, 3.3 · Mo, 1.65 · W, 16 · N.

Rounding

PREN – 1 decimal place, contributions – 2 decimal places.

Fillet weld size

Convert fillet weld throat thickness a to leg length z and back.

Formulas

z = a · √2

a = z · √2 / 2

Calculation rules

• Equal-leg fillet weld with a right-angled triangular cross-section (90° between the parts).
• Quick-reference table for values from 2 to 13 mm.

Rounding

2 decimal places.

Intermittent weld segments

Intermittent welds: gap length, total length, drawing designation and clash with an obstacle.

Formulas

e = (L − n · l) / (n − 1)

L = n · l + (n − 1) · e

Designation: n × l (e)

Calculation rules

• Gap length needs at least 2 welds; when n · l > L, the welds do not fit in the length.
• Weld Si occupies [(i − 1) · (l + e); (i − 1) · (l + e) + l] from the start.
• Clash: a weld overlaps the obstacle when it starts before the obstacle ends and ends after the obstacle starts (touching is not a clash).

Rounding

Lengths – 1 decimal place.

Flowmeter reading correction

Actual shielding gas flow when the flowmeter is scaled for a different gas.

Formulas

without viscosity: Q = Q₀ · √(ρ_cal / ρ_act)

with viscosity: Q = Q₀ · √(ρ_cal · η_act / (ρ_act · η_cal))

Calculation rules

• Q₀ – flowmeter reading, ρ – density [kg/m³], η – dynamic viscosity [µPa·s]; “cal” – the gas the flowmeter is scaled for, “act” – the actual gas.
• Gas density and viscosity as listed in the calculator table: density at 0 °C and 1013 hPa, viscosity at about 20 °C; for mixtures, density is the composition-weighted mean and viscosity follows Wilke’s rule.
• The viscosity variant is an approximation. Results are indicative; for exact settings use the flowmeter manufacturer’s tables.

Rounding

Flow – 2 decimal places, factor – 4 decimal places, difference in % – 1 decimal place.