Cable Size Chart & Current Rating Table — mm² to AWG, Amps by Size

Key Takeaway

Find the right cable size fast. Full current rating tables (IEC 60364), mm² to AWG conversion, voltage drop data, and derating factors. Copper & aluminium, 1.5mm² to 1000mm². Backed by 20+ years of cable manufacturing experience.

Selecting the correct cable size is the single most critical decision in any electrical installation. Undersized cable overheats, trips breakers, causes voltage drop problems, and creates fire hazards. Oversized cable wastes money — copper and aluminium are expensive materials. This guide gives you everything you need to size cables correctly: complete mm² to AWG conversion tables, current rating charts for both copper and aluminium conductors, voltage drop calculations, and practical selection methods used by engineers worldwide.

Whether you are designing a power distribution network in Africa, wiring an industrial plant in Southeast Asia, or specifying cables for a construction project in the Middle East — the tables in this article will be your daily reference.

Cable Size Chart: mm² Cross-Section Area (IEC Standard)

The international standard (IEC 60228) defines cable sizes by conductor cross-sectional area in square millimetres (mm²). This is the system used across Europe, Africa, Asia, Middle East, and most of the world outside North America.

Standard IEC Cable Sizes

The preferred sizes per IEC 60228 are:

Small sizes (lighting, control, instrumentation): 0.5 — 0.75 — 1.0 — 1.5 — 2.5 — 4 — 6 — 10 mm²

Medium sizes (power distribution, motors): 16 — 25 — 35 — 50 — 70 — 95 — 120 mm²

Large sizes (main feeders, transmission): 150 — 185 — 240 — 300 — 400 — 500 — 630 — 800 — 1000 mm²

These are nominal sizes — the actual measured cross-section may vary slightly due to conductor construction (solid vs stranded) and manufacturing tolerances (IEC 60228 allows up to +2% resistance tolerance).

mm² to AWG Conversion Chart

North America uses the American Wire Gauge (AWG) and kcmil system instead of mm². If you are working with equipment rated in AWG or sourcing cable for projects that specify AWG, use this conversion table:

AWG/kcmil	mm² (exact)	mm² (nearest IEC)	Conductor Ø (mm)	Typical Use
18 AWG	0.823	0.75	1.02	Thermostat, signal wire
16 AWG	1.31	1.5	1.29	Light fixtures, extension cords
14 AWG	2.08	2.5	1.63	15A branch circuits
12 AWG	3.31	4	2.05	20A branch circuits
10 AWG	5.26	6	2.59	30A circuits, dryers
8 AWG	8.37	10	3.26	40A circuits, ranges
6 AWG	13.3	16	4.11	55A, large appliances
4 AWG	21.2	25	5.19	70A feeders
2 AWG	33.6	35	6.54	95A feeders
1 AWG	42.4	50	7.35	110A feeders
1/0 (0) AWG	53.5	50	8.25	125A service entrance
2/0 (00) AWG	67.4	70	9.27	145A service entrance
3/0 (000) AWG	85.0	95	10.40	165A feeders
4/0 (0000) AWG	107.2	120	11.68	195A main feeders
250 kcmil	127	120	12.70	215A
350 kcmil	177	185	15.02	260A
500 kcmil	253	240	17.96	320A
750 kcmil	380	400	22.00	400A
1000 kcmil	507	500	25.43	475A

Key conversion formula:

• AWG to mm²: Area (mm²) = 0.012668 × 92^((36 − AWG)/19.5)
• mm² to AWG: AWG = 36 − 19.5 × log(Area/0.012668) / log(92)

Important note: AWG and mm² sizes do not align exactly. When substituting, always use the next larger IEC size to ensure adequate current capacity. For example, 6 AWG (13.3mm²) should be replaced with 16mm², not 10mm².

Cable Current Rating Chart — Copper Conductors

Current ratings (ampacity) depend on insulation type, installation method, ambient temperature, and grouping. The following tables are based on IEC 60364-5-52 (equivalent to BS 7671) reference conditions.

Single-Core Copper Cable — Current Ratings by Installation Method

Reference conditions: 30°C ambient air, 20°C ground temperature, thermal resistivity of soil 2.5 K·m/W.

Three-Core/Four-Core Copper Cable — Current Ratings

For multicore cables (3-core or 4-core), ratings are lower due to mutual heating between conductors.

Installation method definitions:

• Method A1: Cable in conduit embedded in thermally insulating wall — worst case, lowest rating
• Method B1: Cable in conduit fixed to wall surface or ceiling — moderate heat dissipation
• Method C: Cable clipped directly to wall/ceiling without conduit — good air exposure
• Method D: Cable buried directly in ground — soil acts as heat sink
• Method E: Single cable in free air — best heat dissipation, highest rating

Cable Current Rating Chart — Aluminium Conductors

Aluminium has approximately 61% the conductivity of copper. For the same current, aluminium cable needs a larger cross-section — typically 1.6× the copper area.

Copper vs Aluminium — quick equivalents for project budgeting:

Voltage Drop Calculation & Cable Sizing

Current rating alone does not determine cable size. For long cable runs, voltage drop often becomes the controlling factor — especially in Africa, Southeast Asia, and rural electrification projects where distribution distances are long.

Maximum Allowable Voltage Drop

Voltage Drop Formula

For AC single-phase circuits: Vd = 2 × I × L × (R·cosφ + X·sinφ) / 1000

For AC three-phase circuits: Vd = √3 × I × L × (R·cosφ + X·sinφ) / 1000

Where:

• Vd = voltage drop (V)
• I = current (A)
• L = cable length one way (m)
• R = AC resistance (Ω/km) at operating temperature
• X = reactance (Ω/km) — typically 0.08 Ω/km for multicore, 0.09–0.12 for single-core with spacing
• cosφ = power factor (typically 0.85 for motors, 1.0 for resistive loads)

Voltage Drop Table — Copper Cable (mV/A/m)

This table gives voltage drop per ampere per metre for copper cables at 70°C conductor temperature, power factor 0.8:

Practical Example — Sizing by Voltage Drop

Project: 3-phase motor, 45kW, 400V, power factor 0.85, cable run 120 metres, installed in conduit on wall.

Step 1: Calculate current I = 45,000 / (√3 × 400 × 0.85) = 76.5A

Step 2: Select cable by current rating From the current rating table (Method B1, 3-core): 25mm² carries 101A ✓

Step 3: Check voltage drop Using mV/A/m table: 25mm² three-phase = 1.50 mV/A/m Vd = 76.5 × 120 × 1.50 / 1000 = 13.8V Percentage: 13.8 / 400 × 100 = 3.4% ✓ (under 5% limit)

Result: 25mm² copper cable is adequate for both current and voltage drop.

If the run was 250 metres: Vd = 76.5 × 250 × 1.50 / 1000 = 28.7V = 7.2% ✗ (exceeds 5%) Need to upsize to 35mm²: Vd = 76.5 × 250 × 1.10 / 1000 = 21.0V = 5.3% — still borderline Upsize to 50mm²: Vd = 76.5 × 250 × 0.80 / 1000 = 15.3V = 3.8% ✓

This demonstrates why long cable runs in industrial and infrastructure projects often require larger sizes than current rating alone would suggest.

Cable Size Selection by Load (kW)

For quick reference, here is a cable size guide based on load power for common voltages:

Three-Phase 400V System — Copper Cable

Single-Phase 230V System — Copper Cable

Important: These tables assume standard installation conditions (30°C ambient, single circuit, no grouping). Apply derating factors for hot climates, grouped cables, or thermal insulation proximity.

Derating Factors: When Standard Ratings Don't Apply

Real-world installations rarely match reference conditions perfectly. Apply these correction factors to the standard current ratings:

Ambient Temperature Correction (Air)

Critical for hot climates: In regions where ambient temperatures regularly exceed 40°C (Middle East, sub-Saharan Africa, South Asia), you must derate cable current capacity. A cable rated 100A at 30°C ambient only carries 87A at 40°C with PVC insulation. This is why XLPE insulation is strongly preferred for hot climate installations — it loses less capacity at elevated temperatures.

Grouping Correction Factors

When multiple cables run together, mutual heating reduces each cable's capacity:

Soil Temperature & Thermal Resistivity Correction (Buried Cables)

Cable Construction: How Size Relates to Physical Dimensions

Cable cross-section is just the conductor area. The overall cable diameter depends on insulation thickness, armouring, and sheath:

Typical Overall Dimensions — 4-Core Armoured XLPE Cable (0.6/1kV)

Why this matters for procurement:

• Overall diameter determines conduit size, duct space, and bending radius
• Weight per km determines shipping cost (container loading) and drum size
• A 4×240mm² SWA cable weighs 10.6 tonnes per km — that's roughly one 20ft container per 2km of cable

Short-Circuit Current Rating

Cable must also withstand short-circuit current without damage. The adiabatic equation determines the minimum cable size for fault protection:

Minimum size = I²t / k²

Where:

• I = fault current (A)
• t = disconnection time (s)
• k = material constant (copper/PVC = 115, copper/XLPE = 143, aluminium/PVC = 76, aluminium/XLPE = 94)

Maximum Short-Circuit Current by Cable Size (1 Second Duration)

Cable Sizing Checklist for Engineers

Use this systematic approach for every cable sizing decision:

Step 1: Determine design current (IB)

• Calculate from load: IB = P / (V × cosφ) for single-phase, or P / (√3 × V × cosφ) for three-phase
• Include starting current surges for motors (6–8× FLC for DOL start)

Step 2: Select protective device rating (IN)

• IN must be ≥ IB
• Standard ratings: 6, 10, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250A

Step 3: Select cable size for current capacity (IZ)

• IZ must be ≥ IN (cable must carry at least the fuse/breaker rating)
• Apply derating factors: ambient temperature × grouping × installation method
• Effective capacity = table value × all applicable factors

Step 4: Verify voltage drop

• Calculate Vd using mV/A/m values × current × length
• Must be within allowable limit (typically 5% for power circuits)
• If voltage drop exceeds limit, increase cable size

Step 5: Verify short-circuit rating

• Cable must withstand maximum prospective fault current for disconnection time
• Minimum size from adiabatic equation must be ≤ selected size

Step 6: Verify earth fault loop impedance

• For overcurrent protective devices, the fault loop impedance must be low enough to ensure disconnection within required time (0.4s for final circuits, 5s for distribution)

Final size = largest of Step 3, 4, 5, and 6 results

Frequently Asked Questions

What size cable do I need for 100 amps?

For 100A in a three-phase system: 25mm² copper (clipped direct) or 35mm² aluminium. If installed in conduit in wall, you need 35mm² copper. Always verify voltage drop for runs over 30 metres.

How do I convert AWG to mm²?

The most common conversions: 14 AWG ≈ 2.5mm², 12 AWG ≈ 4mm², 10 AWG ≈ 6mm², 8 AWG ≈ 10mm², 6 AWG ≈ 16mm², 4 AWG ≈ 25mm², 2 AWG ≈ 35mm², 1/0 AWG ≈ 50mm², 4/0 AWG ≈ 120mm². Always round UP to the next IEC size when substituting.

Is 4mm cable OK for a 32A circuit?

No. 4mm² copper in conduit in wall (Method A1) is only rated 26A — below the 32A protective device rating. You need 6mm² minimum (rated 34A in the same condition). This is a common mistake that causes cable overheating.

What is the difference between cable size and wire gauge?

Cable size (mm²) describes the cross-sectional area of the conductor — it directly tells you the amount of conducting material. Wire gauge (AWG) is an arbitrary numbering system where smaller numbers mean larger wires. mm² is the international standard (IEC); AWG is used in North America.

How does cable length affect size selection?

Longer cables have more resistance, causing greater voltage drop. For short runs (under 20m), current rating alone usually determines size. For runs over 50m, voltage drop almost always forces you to use a larger cable than current alone requires. A 50m run may need one size up; a 200m run may need two or three sizes up.

Why use XLPE insulation instead of PVC for larger cables?

XLPE-insulated cables have a higher continuous operating temperature (90°C vs 70°C for PVC), which means approximately 15–20% more current capacity at the same conductor size. For cables 50mm² and above, the additional capacity of XLPE often allows you to use a smaller conductor — saving material cost that more than offsets the slightly higher insulation cost.

What cable size for a 200m run at 50A?

At 50A over 200m three-phase (400V), using mV/A/m method:

• 25mm²: Vd = 50 × 200 × 1.50/1000 = 15.0V = 3.75% ✓
• But verify current rating: 25mm² clipped direct = 112A > 50A ✓
• 25mm² is adequate for both current and voltage drop in this case.

For single-phase 230V at the same distance: you would likely need 70mm² due to higher voltage drop percentage.

Related Products & Resources

Cable Products for Your Project

• XLPE Power Cable — 0.6/1kV to 35kV, copper or aluminium conductor
• 4-Core Armoured Cable (SWA) — Steel wire armoured for direct burial
• PVC Control Cable — Multi-core control and instrumentation
• Aerial Bundled Cable (ABC) — Overhead distribution 0.6/1kV

Related Technical Guides

• 3 Phase Power Cable Sizes Chart — Detailed three-phase sizing with specifications
• 4 Core Armoured Cable Specifications — Size chart, current ratings, and pricing
• Cable Insulation Types Comparison — PVC vs XLPE vs LSZH performance data
• Underground Power Cable Types — Direct burial cable selection
• Medium Voltage Cable 11kV & 33kV — MV cable sizing and specifications

Get the Right Cable for Your Project

Need help selecting cable sizes for your project? Send us your load schedule or single-line diagram and our engineering team will provide:

• Cable size recommendations for every circuit
• Voltage drop verification
• Bill of quantities with pricing
• Technical datasheets for specified cables

We manufacture all standard sizes from 1.5mm² to 1000mm² in copper and aluminium, with PVC or XLPE insulation, armoured or unarmoured. IEC 60502, BS 5467, and GB/T 12706 certified.