Electroforming Amperage Calculator
Set the exact current for a clean, even deposit — from your metal and surface area to the amps on the dial, the safe range, and the hours to your target thickness.
Units shown in ASI (A/in²). The recommended point gives slow, bright, even growth; the maximum needs strong agitation.
How the electroforming amperage calculator works
Electroforming is deceptively simple to state and unforgiving to get wrong: you pass a direct current through a bath so that metal ions leave the anode and build up, atom by atom, on the surface of your object — the cathode. Whether the result is a smooth, bright, structurally sound shell or a burnt, granular, dendrite-covered mess comes down almost entirely to one number: the current density, the amount of current flowing through each unit of surface area. Set it right and the deposit nucleates in fine, even grains. Set it too high and the piece burns; too low and it turns dull and salmon-coloured. This tool exists to get that number right, and to show every step so you can trust it.
The calculator works in three linked stages. The Amperage tab turns a metal choice and a surface area into the current you dial into your rectifier, with a recommended value and a maximum safe ceiling. The Surface Area tab helps you measure that area — the hardest part for organic pieces — either by adding up simple shapes or by the professional foil-weight trick. The Time to Thickness tab uses Faraday's law of electrolysis to tell you how many hours in the bath it takes to grow a given thickness, corrected for the bath's real efficiency.
Current density: the one number that decides everything
Current density is usually written in amps per square inch (ASI) or amps per square decimetre (A/dm²). Each metal and bath has a band that produces good deposits. The amperage you actually set is simply that density multiplied by the total surface area:
Amperage (A) = current density × surface area
For copper in a standard acid-sulfate bath the globally recognised starting point is 0.1 ASI, which is about 1.55 A/dm² or 0.0155 A/cm². That is a median, not a law: highly detailed organic textures often plate better nearer 0.05 ASI, where slow, gentle growth captures fine surface detail, while higher densities plate faster but demand aggressive agitation to keep fresh ions arriving at the surface. The table below gives the working bands this calculator uses.
| Metal | Typical density (ASI) | Metric (A/dm²) | Notes |
|---|---|---|---|
| Copper | 0.05 – 0.30 | 0.8 – 4.6 | Acid sulfate; 0.10 ASI is the classic starting point |
| Silver | 0.03 – 0.12 | 0.5 – 1.9 | Lower band — burns and forms nodules easily |
| Nickel | 0.13 – 0.32 | 2.0 – 5.0 | Sulfamate baths sustain high density with agitation |
| Gold | 0.03 – 0.10 | 0.5 – 1.6 | Thin decorative deposits; efficiency often ~90% |
Measuring surface area, including organic objects
Amperage is only as good as the surface-area figure behind it. For uniform objects, geometry does the job, and the calculator applies the right formula automatically — doubling a flat sheet for its two faces, wrapping a cylinder's side plus optional ends, and so on. The genuinely hard case is the leaf, crystal, insect wing or 3D-printed figurine that has no formula at all.
The segmentation method
Break the awkward object into simple shapes you can measure, run each through the builder, and add them up. A pendant that is a cylinder joined to a flat base is just a cylinder plus a sheet. It is approximate, but for many pieces it lands within a few percent — close enough, because the amperage band itself spans a range.
The foil-weight method
This is what professional shops use for irregular work, and it is beautifully simple. Wrap the object tightly in ordinary aluminium foil and trim the foil flush so it mirrors the surface exactly. Weigh that foil on a jeweller's scale. Then cut a precise 10 × 10 cm square — 100 cm² — of the same foil and weigh it too. Because foil has a constant weight per unit area, the object's area is:
Surface area = 100 cm² × (weight of object foil ÷ weight of the 10×10 square)
It sidesteps geometry entirely and is often the most accurate figure you can get for a complex piece.
Time to thickness: Faraday's law
Once the current is set, how long until the shell is thick enough to be strong? Faraday's law of electrolysis ties deposited mass directly to the electric charge passed. Rearranged for thickness, the calculator uses:
time = (thickness × density × area) ÷ (current × equivalent weight ÷ Faraday’s constant × efficiency)
where the equivalent weight is the metal's atomic weight divided by its valence, and Faraday's constant is 96,485 coulombs per mole of electrons. The one input people forget is current efficiency: not every electron reduces a metal ion. Some split water and evolve hydrogen gas instead. Copper and nickel sulfamate baths run at a highly efficient 95–100%, gold nearer 90%, and hard chrome below 20% — so assuming 100% efficiency quietly under-plates the part. As a feel for the numbers, copper at 0.1 ASI grows roughly 20 microns of thickness per hour.
Getting a clean deposit: the practical levers
Run the rectifier in constant-current mode
This is the single most common beginner failure. A benchtop DC supply can hold either a fixed voltage or a fixed current. Electroforming needs constant current (CC). As the deposit grows the cathode area rises and the bath resistance shifts; a supply locked to constant voltage would let the current climb by Ohm's law and burn the piece over a long run. In CC mode the supply trims the voltage automatically to hold your amperage exactly. Set the voltage limit high and dial the current down to the calculated target.
Tame the edge effect
Current crowds onto edges and sharp points because more field lines converge there, so those spots plate faster and can burn into nodules or treeing while the centre is still building. Lowering the average density, increasing anode-to-cathode distance, and adding a sacrificial auxiliary cathode — a conductive ring or frame that soaks up the excess current — all push the deposit toward uniform thickness. Chemists describe a bath's ability to plate evenly over an irregular shape as its throwing power, captured by the dimensionless Wagner number; a higher number means better secondary current distribution and a more uniform shell.
Agitate, and mind the wire
Agitation — magnetic stirring or air sparging — thins the depleted boundary layer at the cathode and lets you run higher current without burning. And don't starve the piece through a too-thin suspension wire: a hair-thin wire leaves a smaller contact mark but its resistance robs current before it reaches the work, quietly under-plating it. Size the wire so the voltage drop to the cathode stays small.
A note on scope and safety. These are planning figures drawn from standard electroforming practice; real baths vary with temperature, chemistry, agitation and additives, so treat the output as a well-founded starting point and refine from test results. Electroforming uses electricity and chemical baths — some acidic, some containing cyanide in commercial gold systems — that demand proper ventilation, gloves, eye protection and correct disposal. Follow your bath supplier's safety data and local regulations.
FAQ
How many amps do I need for copper electroforming?
The standard starting point is 0.1 amps per square inch of surface, about 1.55 A/dm². A 3 in² piece needs roughly 0.3 amps, set in constant-current mode. Fine organic textures often plate better near 0.05 ASI; higher currents need strong agitation to avoid burning.
Why is my electroformed copper salmon pink and dull?
Almost always the current density is too low for the true surface area, so growth is coarse and granular rather than finely nucleated — or the bath is low on brightener. Re-measure the area, raise the current toward 0.1 ASI, and confirm the rectifier is holding steady current, not fixed voltage.
Should the rectifier be on constant current or constant voltage?
Constant current. As the deposit grows, resistance changes, and a constant-voltage supply would let the current drift up and burn the piece. Constant-current mode adjusts voltage automatically to hold your amperage. Set the voltage limit to a safe maximum and dial the current down to target.
How do I find the surface area of an irregular object?
Two ways. Segmentation adds up simple shapes — cylinders, boxes, spheres. The foil-weight method is more accurate for organic pieces: wrap the object in foil, trim flush, weigh it, then weigh a 10×10 cm square of the same foil. Area = 100 cm² × (object-foil weight ÷ square weight).
How long does it take to reach a given thickness?
It follows Faraday's law and depends on metal, current, area and efficiency. Copper at 0.1 ASI builds roughly 20 microns per hour. The Time-to-Thickness tab inverts Faraday's law for the exact hours, and lets you drop efficiency below 100% to account for hydrogen evolution and other losses.
What causes burning and treeing at the edges?
Current concentrates at edges and points — the edge effect, or dogboning — spiking local density into nodules or branching dendrites. Lower the average density, agitate well, increase anode-to-cathode distance, and add a sacrificial auxiliary cathode or wire frame to absorb the excess current.