Portlandia Electric Supply · Technical Team · Updated September 4, 2026

Milliamps show up everywhere in modern electrical work: sensor loops, CT secondaries, LED drivers, BMS standby draw, GFCI trip thresholds. Amps are what breakers, fuses, and wire are sized in. Converting between them is a one-step division — but applying the result correctly is where real design decisions happen. Use the calculator below, then keep reading for the formula, reference charts, and the NEC rules that turn a conversion into a code-compliant circuit.

The conversion is a pure metric prefix shift. The ampere (A) is the SI base unit of electric current; the milliampere (mA) is one-thousandth of an ampere:

Amps = Milliamps ÷ 1,000   ·   Milliamps = Amps × 1,000

Two mental shortcuts make this instant in the field. First, dividing by 1,000 moves the decimal point three places left: 4,700 mA becomes 4.7 A. Second, any milliamp value under 1,000 is a fraction of an amp — 250 mA is 0.25 A, a quarter of an amp. If your converted number comes out larger than the milliamp number, you multiplied instead of dividing; flip it.

This is the reverse of the power-focused conversion in our amps-to-watts guide, and it pairs naturally with kWh-to-amps when you are moving between energy billing units and circuit current. Neither of those requires voltage; this one doesn't either. mA-to-amps is a same-quantity conversion — current to current — so no voltage, resistance, or power factor ever enters the math.

The most common conversions, pre-computed. Bookmark this table — these are the values that show up on labels and datasheets daily.

Table 1 — Quick mA→A reference. Divide by 1,000 to reproduce any row.

1. GFCI and personnel protection thresholds

The most consequential milliamp number in the trade is 4–6 mA — the trip window UL 943 sets for Class A ground-fault circuit interrupters. At 5 mA (0.005 A), a GFCI must trip fast enough to prevent ventricular fibrillation. Equipment-protection GFCIs trip at 20 mA, and the 30 mA RCD class common in international installations sits between the two. Every one of these safety thresholds is specified in milliamps while the circuit it protects is rated in amps — the conversion is the bridge between the protection spec and the conductor design.

2. Solar monitoring, CTs, and control circuits

Current transformers output standardized secondary signals — 5 A, 1 A, or 333 mV at full scale — and many revenue-grade meters and data loggers express burden and loop current in milliamps. The 4–20 mA analog loop standard used for irradiance sensors, temperature probes, and BMS communication lives entirely in milliamp territory. When commissioning a microinverter system or a monitoring gateway, you will convert mA loop readings to amps to validate that the sensor chain matches the array's actual string current.

3. Battery and BMS parasitic draw

A lithium battery's BMS typically draws 20–200 mA in standby. Over a month, a 100 mA (0.1 A) parasitic draw on a 12 V system consumes about 72 Ah — enough to noticeably drain a 100 Ah battery sitting in storage. This is why our battery maintenance guide recommends disconnecting or maintaining charge on stored banks, and why the battery runtime calculator asks about always-on loads.

4. LED drivers and low-voltage lighting

Constant-current LED drivers are rated in milliamps: 350 mA, 500 mA, 700 mA, 1,050 mA are standard drive currents. Selecting the driver, then the supply, then the branch protection means walking the same number through three unit conventions — mA at the LED, watts at the driver input, amps at the breaker.

The National Electrical Code rarely speaks in milliamps — its tables are denominated in amperes — but several articles anchor to milliamp-scale phenomena:

• NEC 210.8 / UL 943 (GFCI): personnel protection trips at 4–6 mA. Equipment ground-fault protection (NEC 210.13, 215.10, 240.13) acts at 20 mA or higher.
• NEC 240.6 (Standard ratings): after converting a milliamp load to amps, overcurrent devices come in fixed steps — 15, 20, 25, 30 A and up for branch circuits, with fractional ratings available as fuses. The calculator above applies the 125% rule and rounds to the next standard size automatically.
• NEC 725 (Class 2/3 control circuits): the milliamp domain of thermostats, sensors, and relay coils, with power-limited sources often rated in VA and currents measured in mA.
• NEC 690.8 (PV circuit sizing): module Isc printed as 10,850 mA becomes 10.85 A before the 125% irradiance factor and the second 125% continuous factor are applied.

Once your load is in amps, the next decision is conductor ampacity. Our NEC 310.16 ampacity chart and the NEC wire sizing guide take the converted amp value and return a gauge; THHN copper and PV wire cover most solar and branch-circuit pulls.

Table 2 — Milliamp load → amps → NEC 125% design current → standard overcurrent device → minimum conductor (copper, 75 °C, before derating).

Table 3 — Current units span nine orders of magnitude. kA appears on breaker nameplates as interrupting capacity, not load.

Table 4 — Real devices, both unit conventions, one conversion rule.

• Amps to Watts: Convert Current to Power
• Kilowatt-Hours to Amps Guide
• Wire Ampacity Chart (NEC 310.16)
• NEC Wire Sizing Guide
• Solar Wire & Cable Guide: PV Wire vs USE-2 vs THHN
• Solar Disconnect & Overcurrent Protection (NEC 690)
• Surge Protection for Solar Systems
• Solar Charge Controller Sizing Guide
• How to Size Circuit Breakers: NEC 125% Rule
• Battery Backup Runtime Calculator
• Shop Cerro THHN Wire
• Shop PV Wire
• Shop Circuit Breakers
• Shop Microinverters

Need breakers, wire, or protective devices sized for your converted load? Get a quote from Portlandia Electric Supply — we stock circuit breakers, THHN wire, and full solar kits with same-day shipping on most items.