Welding Calculator - Current, Voltage & Heat Input
Calculate welding current, voltage, travel speed, and heat input for MIG, TIG, Stick, and Flux-Cored welding from material thickness or welding current.
Welding Calculator
Input Parameters
Calculated Parameters
Heat input above is arc energy, the AWS D1.1 and ASME IX convention: (volts x amps x 60) / (1000 x travel speed in mm/min). ISO heat input applies the thermal efficiency factor k from EN ISO 1011-1: k is 0.8 for MIG, Stick and Flux-Cored, and 0.6 for TIG. Report the value that your welding code requires.
Calculation Formulas
Heat Input (Q) = (V × I × 60) / (1000 × S)
Q = (V × I × 60) / (1000 × S)
Where:
V = Voltage (18.8 V)
I = Current (120 A)
S = Travel Speed (240 mm/min)
Q = (18.8 × 120 × 60) / (1000 × 240) = 0.56 kJ/mm
HI = 0.8 × 0.56 = 0.45 kJ/mm
Current Calculation for MIG:
I = thickness × 40
I = 3 × 40 = 120 A
Voltage Calculation for MIG:
V = 14 + (I / 25)
V = 14 + (120 / 25) = 18.8 V
Travel Speed Calculation for MIG:
S = 300 - (thickness × 20)
S = 300 - (3 × 20) = 240 mm/min
Documentation
Welding calculator
A welding calculator estimates the current, voltage, travel speed, and heat input needed for an arc weld. It works from the material thickness and the welding process being used. This tool covers four common processes: MIG (GMAW), TIG (GTAW), Stick (SMAW), and flux-cored (FCAW).
The results are rules of thumb, not a certified welding procedure. They hold for thin material welded in a single pass. On thicker material the underlying formulas leave their valid range. When that happens, the calculator shows a warning instead of a number, rather than guess.
How the calculator works
Enter a material thickness in millimeters and pick a welding process. The calculator computes a recommended current, then works out voltage and travel speed from that current and thickness. A current can also be typed in directly. In that case the calculator works backward to estimate the thickness the process suits, then derives the rest.
Welding current formula
Current rises in a straight line with thickness. The rate differs by process:
- MIG: I = thickness × 40
- TIG: I = thickness × 30
- Stick: I = thickness × 35
- Flux-cored: I = thickness × 38
I is current in amps. Thickness is in millimeters.
Welding voltage formula
Voltage rises with current:
- MIG: V = 14 + I / 25
- TIG: V = 10 + I / 40
- Stick: V = 20 + I / 50
- Flux-cored: V = 22 + I / 30
Travel speed formula
Travel speed is how fast the torch or electrode moves along the joint, measured in millimeters per minute. It falls as material gets thicker:
- MIG: S = 300 − thickness × 20
- TIG: S = 150 − thickness × 10
- Stick: S = 200 − thickness × 15
- Flux-cored: S = 250 − thickness × 18
Heat input formula
Heat input measures the thermal energy delivered per millimeter of weld, in kilojoules per millimeter (kJ/mm). AWS D1.1 and ASME IX define it as arc energy:
Q = (V × I × 60) / (1000 × S)
V is voltage, I is current in amps, S is travel speed in mm/min.
A second figure, ISO heat input, comes from EN ISO 1011-1. It multiplies arc energy by a thermal efficiency factor, k. This factor is a number below 1. It estimates how much of the arc's energy actually enters the metal, rather than being lost as radiation or spatter.
ISO heat input = k × Q
k is 0.8 for MIG, Stick, and flux-cored welding. It is 0.6 for TIG, because a TIG arc transfers less of its energy into the base metal than the other three processes. Welding codes differ on which figure they call "heat input." Report whichever one the applicable code requires.
Why some inputs give no result
The current, voltage, and travel-speed formulas are straight-line approximations. They only hold for thin material welded in a single pass. Real arc welding runs at roughly 0.5 to 5 kJ/mm of heat input. Above that ceiling, no single-pass procedure exists. The joint needs multiple passes, each one kept inside that range.
The calculator checks this. If a thickness and process combination would need an arc energy above 5 kJ/mm, it shows a warning instead of a number. It does the same if the formula gives a travel speed of zero or less. Welding to a value the calculator has not shown risks burn-through, excess distortion, or a joint that fails inspection.
Example
A welder is joining 5 mm mild steel plate with MIG.
- Current: 5 × 40 = 200 A
- Voltage: 14 + 200 / 25 = 22 V
- Travel speed: 300 − 5 × 20 = 200 mm/min
- Arc energy (AWS/ASME heat input): (22 × 200 × 60) / (1000 × 200) = 1.32 kJ/mm
- ISO heat input: 0.8 × 1.32 = 1.06 kJ/mm
Both figures fall inside the 0.5–5 kJ/mm band a single MIG pass can produce, so the calculator returns a result.
Compare that with 10 mm steel welded the same way. The formulas call for 400 A, 30 V, and a travel speed of 100 mm/min. That works out to an arc energy of 7.2 kJ/mm, above the 5 kJ/mm ceiling. The calculator shows a warning instead of these numbers. A real weld on 10 mm steel needs multiple passes under a qualified procedure, not a single-pass estimate.
Typical current and thickness ranges by process
| Process | Typical current | Typical thickness | Common use |
|---|---|---|---|
| MIG (GMAW) | 50–400 A | 0.5–6 mm | General fabrication, automotive |
| TIG (GTAW) | 5–300 A | 0.5–3 mm | Precision work, thin material |
| Stick (SMAW) | 50–300 A | 3–25 mm | Construction, field repair |
| Flux-cored (FCAW) | 75–350 A | 3–25 mm | Outdoor work, thick sections |
These ranges describe common shop practice. The calculator's formulas extend the same straight-line rule across each process, regardless of a specific machine's limits.
Frequently asked questions
What is heat input in welding? Heat input is the thermal energy delivered per millimeter of weld, in kJ/mm. It affects how deep the weld penetrates, how fast it cools, and how much the surrounding metal's structure changes.
What is the difference between AWS heat input and ISO heat input? AWS D1.1 and ASME IX heat input is arc energy: voltage times current times 60, divided by 1000 times travel speed. ISO 1011-1 heat input multiplies that figure by a thermal efficiency factor, k. The factor is 0.6 for TIG and 0.8 for the other three processes. It gives a lower number that better reflects the energy the joint actually absorbs.
Why does the calculator show a warning instead of a result? The formulas are straight-line rules that only work for thin material welded in one pass. Past an arc energy of about 5 kJ/mm, or when the formula gives a travel speed of zero or below, no single-pass weld matches the number. The calculator withholds the result rather than show a false one.
Can I enter current instead of thickness? Yes. Entering a current makes the calculator estimate the thickness that current suits, then compute voltage, travel speed, and heat input from there.
Do these formulas work for aluminum? The formulas are based on steel welding practice. Aluminum conducts heat away faster than steel, so it generally needs around 30% more current than steel of the same thickness, along with pure argon or an argon-helium shielding gas.
Is this a substitute for a welding procedure specification (WPS)? No. For code-governed work, a qualified WPS, tested and documented for the specific joint and material, takes precedence. The calculator gives a starting point for initial setup, not a certified procedure.
References
- American Welding Society. AWS D1.1/D1.1M Structural Welding Code — Steel.
- International Organization for Standardization. EN ISO 1011-1, Recommendations for welding of metallic materials.
- Jeffus, L. Welding: Principles and Applications, 8th ed. Cengage Learning, 2021.
- TWI Ltd. "Calculating Heat Input." twi-global.com.