Enter the total square footage, minutes, and thickness in mils into the calculator to determine the anodizing amperage.
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Anodizing Amperage Formula
The calculator uses two formulas. Rectifier Setup gives the amps to dial in and the run time. The 720 Rule Solver relates thickness, time, and current density.
Amps = ASF × Area_sqft Time_min = 720 × Thickness_mil / ASF
- Amps — rectifier output current
- ASF — current density in amps per square foot
- Area_sqft — total wetted surface area of the parts and rack contact
- Thickness_mil — target coating thickness in mils (1 mil = 25.4 µm)
- Time_min — anodize dwell time in minutes
The 720 rule assumes ~100% current efficiency in a standard sulfuric acid bath at typical operating temperature. Real efficiency varies with bath chemistry, temperature, alloy, and agitation, so add 5 to 15% to the calculated time when in doubt. To convert ASF to ASD (A/dm²), divide by 9.2903.
Reference Values
Typical current density and thickness ranges by anodize type:
| Process | Current Density | Typical Thickness |
|---|---|---|
| Type II Decorative | 10–15 ASF | 0.1–0.4 mil |
| Type II Architectural | 12–18 ASF | 0.4–0.8 mil |
| Type III Hardcoat | 24–30 ASF | 1.0–2.0 mil |
| Type III Heavy Build | 30–36 ASF | 2.0–4.0 mil |
Quick run-time lookup using the 720 rule:
| Thickness | @ 12 ASF | @ 18 ASF | @ 24 ASF |
|---|---|---|---|
| 0.5 mil | 30 min | 20 min | 15 min |
| 1.0 mil | 60 min | 40 min | 30 min |
| 2.0 mil | 120 min | 80 min | 60 min |
Worked Example
You have 8 square feet of 6061 parts and want a 2 mil hardcoat at 24 ASF.
- Amps = 24 × 8 = 192 A
- Time = 720 × 2 / 24 = 60 minutes
- Total charge = 192 × 1 = 192 A·hr
Why does my actual thickness come up short? Current efficiency drops as the coating builds and as bath temperature rises. Hardcoat baths run cold (28–40°F) precisely to keep efficiency near 100%. If you are short, extend time before raising current.
Should I ramp the current? Yes for hardcoat. Ramp from 0 to full ASF over 5–15 minutes to avoid burning. The 720 rule time is measured from when full current is reached.
ASF or ASD? ASF is amps per square foot, common in North America. ASD is amps per square decimeter, common elsewhere. 1 ASD = 9.29 ASF.
