Short answer: 4× #10 AWG THHN + 1× #6 AWG THHN ground in 3/4" EMT uses 0.135 sq in of fill in a conduit with a 0.213 sq in limit at 40% — that's 25.3% fill, comfortably legal under NEC Chapter 9 Table 1. You could fit another #6 if needed (would put you at ~35%). Below is the line-by-line math from NEC Tables 4 and 5, the alternative pulls if you have to swap to PVC or RMC, and the cases where 3/4" EMT won't work and you have to step up to 1".

The fill rule (NEC Chapter 9 Table 1)

• 1 conductor: 53% maximum fill.
• 2 conductors: 31% maximum fill.
• Over 2 conductors (3+): 40% maximum fill. This is the case for our 5-wire run.

Why 31% for two but 40% for three or more? It's a geometry compromise: two parallel cylinders nested in a circular cross-section leave more wasted space than three or more, so the limit drops to compensate.

EMT internal cross-sectional area (NEC Ch 9 Table 4)

Trade size    OD       ID       Internal area    40% fill (3+ wires)
1/2"          0.706"   0.622"   0.304 sq in     0.122 sq in
3/4"          0.922"   0.824"   0.533 sq in     0.213 sq in   ← our case
1"            1.163"   1.049"   0.864 sq in     0.346 sq in
1-1/4"        1.510"   1.380"   1.496 sq in     0.598 sq in
1-1/2"        1.740"   1.610"   2.036 sq in     0.814 sq in
2"            2.197"   2.067"   3.356 sq in     1.342 sq in
2-1/2"        2.875"   2.731"   5.858 sq in     2.343 sq in
3"            3.500"   3.356"   8.846 sq in     3.538 sq in

THHN/THWN-2 conductor area (NEC Ch 9 Table 5)

Wire size    Approx OD    Cross-section area
14 AWG       0.111"       0.0097 sq in
12 AWG       0.130"       0.0133 sq in
10 AWG       0.164"       0.0211 sq in   ← our case (×4)
8  AWG       0.216"       0.0366 sq in
6  AWG       0.254"       0.0507 sq in   ← our case (×1)
4  AWG       0.324"       0.0824 sq in
3  AWG       0.352"       0.0973 sq in
2  AWG       0.384"       0.1158 sq in
1  AWG       0.446"       0.1562 sq in
1/0          0.486"       0.1855 sq in
2/0          0.532"       0.2223 sq in
3/0          0.584"       0.2679 sq in
4/0          0.642"       0.3237 sq in

Worked example: 4× #10 + 1× #6 THHN in 3/4" EMT

Conductors:
  4 × #10 THHN:    4 × 0.0211 sq in    =    0.0844 sq in
  1 × #6  THHN:    1 × 0.0507 sq in    =    0.0507 sq in
  ─────────────────────────────────────────
  Total fill:                              0.1351 sq in

3/4" EMT capacity (40% fill):              0.213 sq in

Actual fill percentage:
  0.1351 / 0.533 = 25.3%   ←  WELL UNDER 40%   ✓

Verdict: PASS. 3/4" EMT is the right size — comfortable margin.

Step down to 1/2" EMT?

1/2" EMT capacity (40% fill):    0.122 sq in
Our conductors total:             0.1351 sq in

0.1351 > 0.122 by 0.0131 sq in   →  EXCEEDS 40% limit
Actual percentage in 1/2": 44.4%

Verdict: 1/2" EMT does NOT work for this combination. Step up to 3/4".

Step up scenarios — when 3/4" isn't enough

Hypothetical: same circuit, but with 4 × #6 + 1 × #10 ground (instead of 4 × #10):

  4 × #6 THHN:     4 × 0.0507 = 0.2028 sq in
  1 × #10 THHN:    1 × 0.0211 = 0.0211 sq in
  Total:                       0.2239 sq in

3/4" EMT 40% capacity:        0.213 sq in
0.2239 > 0.213  →  EXCEEDS 40% (42% actual fill)

Step up to 1" EMT:
1" capacity (40%):            0.346 sq in
0.2239 / 0.864 = 25.9% fill   ✓ comfortable.

Other conduit types — same conductors, different conduit

Same fill (0.1351 sq in):

3/4" EMT (Sch 40 internal area 0.533):
  0.1351 / 0.533 = 25.3% fill   ✓
3/4" RMC (rigid metal, internal area 0.610):
  0.1351 / 0.610 = 22.1% fill   ✓ (RMC has thicker wall, less ID)
3/4" Sch 40 PVC (internal area 0.581):
  0.1351 / 0.581 = 23.3% fill   ✓
3/4" Sch 80 PVC (internal area 0.508):
  0.1351 / 0.508 = 26.6% fill   ✓
3/4" FMC (flex metal, internal area 0.349):
  0.1351 / 0.349 = 38.7% fill   borderline at 40%

FMC (flexible metal conduit, "Greenfield") has a significantly smaller internal area than EMT/RMC at the same trade size — nearly identical to ENT (smurf tube) and LFNC. If you switch to flex on the last 6 ft into a motor disconnect, recheck fill against the FMC area, not EMT.

Don't forget the wire wrap (THHN OD)

What counts as a conductor?

• Hot, neutral, equipment ground — all count.
• Bare copper ground (NEC 250.122) — counts. Use Table 8 for bare wire size.
• USE-2 / SE / SER cable — the cable jacket OD counts (different rule, NEC 392 if in cable tray).
• Multiconductor cable (e.g., NM-B, MC) — treat the whole cable assembly OD as a single "conductor" under fill rules.

Bends, pull boxes, and 360° total

• NEC 358.26 / 344.26 / 352.26 — no more than 360° of total bends between pull points (boxes or fittings).
• Four 90° bends = 360° max. Anything more requires a pull box.
• Bend radius minimum (Table 2): for 3/4" EMT one-shot bend, 5" minimum to centerline.
• Pulls past 360° without a box are an automatic fail at inspection.

Pull tension and lubrication

• For under 30% fill: dry pull works on most short runs.
• For 30–40% fill: always lubricate with wire-pulling lube (Polywater J, Ideal Yellow 77).
• Maximum pull tension: 0.008 × cmil (NEC 310 commentary). For #6 (26,240 cmil) = ~210 lb max. Fish tape pulls easily exceed this on big wire — use a pulling rope and capstan.
• Avoid pulling on a single hot leg in a multi-conductor pull. Pull all conductors together with a pulling head or a basket grip.

Real-world reasoning behind 4× #10 + 1× #6

This combination is most commonly encountered in:

• Two 240V circuits sharing a conduit: 2 hots + 2 hots + 1 shared neutral or ground. (Add neutrals if not multi-wire branch.)
• 30A subpanel feeder: 2 hots + 1 neutral + 1 ground (4 wires of #10) plus a heavier #6 ground from upstream — uncommon but seen on retrofit work.
• Detached structure feeder: 30A subpanel with separate equipment-grounding conductor #6 size from a remote source.

For the standard case (single-circuit branch run), you'd normally see 2× #10 + 1× #10 ground in 1/2" EMT. The 4-wire-plus-ground configuration in the title is specific to multi-circuit or feeder pulls.

Quick reference table for #10 THHN combos

Conductors                          1/2" EMT    3/4" EMT    1" EMT
2 × #10                              13.9% ✓     7.9% ✓      4.9% ✓
3 × #10                              20.8% ✓    11.9% ✓      7.3% ✓
4 × #10                              27.8% ✓    15.8% ✓      9.8% ✓
4 × #10 + 1 × #10                    34.7% ✓    19.8% ✓     12.2% ✓
4 × #10 + 1 × #6                     44.4% ✗    25.3% ✓     15.6% ✓ ← article
4 × #10 + 2 × #6                     61% ✗     34.8% ✓     21.4% ✓
6 × #10                              41.6% ✗    23.7% ✓     14.6% ✓
8 × #10                              55% ✗      31.6% ✓     19.5% ✓

Run it on your phone

The ElectricianCalc app handles all of Chapter 9: pick the conduit type and size, add conductors by AWG and insulation type, and it returns fill percentage with the over/under verdict instantly. Includes EMT, IMC, RMC, Sch 40 PVC, Sch 80 PVC, FMC, LFMC. 100% offline. Free on the App Store and Google Play.

Related

• Wire size for 40A continuous, 180 ft, 240V single-phase
• Voltage drop and NEC 210.19(A) explained
• NEC wire sizing for branch circuits
• ElectricianCalc — NEC calculator on iOS + Android

Note: Fill rules and conductor areas can shift between NEC editions. Always confirm against the edition your AHJ has adopted. For factory-assembled cable (NM, MC, SER), use the cable assembly OD, not individual conductors.