Conduit Size Calculator Project Checklist

Introduction

Conduit sizing errors are input errors — wrong count, wrong insulation type, wrong conduit type, skipped derating — and inputs are exactly what a checklist catches. Run this checklist after every sizing calculation, before you buy material or pull wire. It takes five minutes and catches the mistakes that cost five hours of rework.

The Conduit Size Calculator does the arithmetic from your conductor list. This checklist verifies everything around the arithmetic: that the list is complete, the tables are the right ones, and the installation realities — bends, derating, supports — have all been checked.

Phase 1: The Conductor List

• ☐ Every hot conductor listed with correct AWG/kcmil size
• ☐ Every neutral listed (shared neutrals counted once, verified against the design)
• ☐ Equipment grounding conductor included in the count
• ☐ Total conductor count confirmed — this number picks the fill limit (1 → 53%, 2 → 31%, 3+ → 40%)
• ☐ Current-carrying conductor count separated — this number drives derating (grounds generally excluded)
• ☐ Insulation type confirmed for each conductor (THHN, XHHW, THW…) — Table 5 areas, not AWG guesses

Phase 2: Wire Size and Derating

• ☐ Wire sized for the load before any conduit math
• ☐ Derating factor applied for the current-carrying count: 80% (4–6), 70% (7–9), 50% (10–20)
• ☐ Derated ampacity ≥ overcurrent protection — wire upsized if not
• ☐ Fill calculation uses the final wire size after any derating-driven upsize

Phase 3: Conduit Size and Type

• ☐ Conduit type selected for the environment (burial, exposure, corrosion, physical damage)
• ☐ Table 4 internal area used for the actual conduit type — not carried over from another type
• ☐ Fill limit from Table 1 matches the conductor count (53%/31%/40%)
• ☐ Smallest passing trade size selected — then judgment-applied (see Phase 5)
• ☐ Mixed-type runs: each segment checked against its own Table 4 values
• ☐ Nipple 60% allowance only used for genuine ≤ 24 in (600 mm) sections
• ☐ Conduit body fill verified separately for each LB, LL, or T in the run

Phase 4: Route and Pull Plan

• ☐ Total bends between pull points ≤ 360° — conduit bodies counted
• ☐ No pull segment designed at the 360° maximum (target 180–270° per segment)
• ☐ Pull boxes or conduit bodies placed at sensible intervals on long runs
• ☐ All conductors planned to feed together with staggered heads (not one at a time)
• ☐ Pulling lubricant on the material list for any 3+ conductor pull
• ☐ Cut ends to be reamed; insulating bushings where required

Phase 5: Judgment and Future-Proofing

• ☐ Upsize considered for runs over ~100 ft (30 m) or ~180° of bend
• ☐ Future circuits considered — spare capacity is cheap now, expensive later
• ☐ Tightest segment (not the average) governs pull difficulty
• ☐ Material takeoff complete: conduit + 10%, wire = length × conductors × 1.10, all fittings, straps, boxes, lube
• ☐ Copper pricing dated; permit fee included in the budget

Phase 6: Compliance

• ☐ Permit pulled (or confirmed not required) with the AHJ before work starts
• ☐ Installation meets the locally adopted NEC edition plus local amendments
• ☐ Support spacing and securing per the raceway’s NEC article
• ☐ Grounding/bonding continuity planned end to end
• ☐ Licensed electrician engaged where the jurisdiction or the work requires it

The compliance checkpoints behind this phase are detailed in the code compliance guide; the error patterns it guards against are catalogued in the common mistakes guide.

Worked Verification Example

Run the checklist against a sample calculation: four 12 AWG THHN conductors in EMT, 40 ft (12.19 m), two 90° bends.

Phase 1: 4 conductors total (3 current-carrying + 1 ground — ground confirmed in the count ✓). Fill limit: 3+ → 40% ✓. Insulation: THHN confirmed, 11.68 mm² each ✓.

Phase 2: 3 current-carrying → no derating ✓. 12 AWG stands ✓.

Phase 3: Total area 4 × 11.68 = 46.72 mm². 1/2″ EMT allows 31.20 mm² — fails; 3/4″ EMT allows 54.80 mm² — passes ✓. 3/4″ EMT at 34.1% fill.

Phase 4: 180° total bends, well under the 360° limit ✓. One pull segment, lubricant on the list ✓.

Phase 5: 40 ft, 180° — short and easy; no upsize needed, though a future circuit would argue for 1″ ✓.

Phase 6: Permit confirmed, straps within 3 ft of boxes, EMT fittings tight ✓.

Imperial cross-check of the fill: 4 × 0.0181 in² = 0.0724 in²; 3/4″ EMT 0.213 in² × 0.40 = 0.0852 in² ≥ 0.0724 — passes at 34.0% fill, matching metric. Checklist complete — buy the material.

Mistakes This Checklist Catches

1. The missing ground. Phase 1 forces it into the count before any math happens.
2. Derating after conduit sizing. Phase 2 comes before Phase 3 — the order is the fix.
3. Carried-over Table 4 values. Phase 3 requires the actual type’s areas, per segment.
4. The 360° body miscount. Phase 4 counts bodies explicitly.
5. Minimum-as-target. Phase 5 forces the upsize question on every run.
6. Permit as afterthought. Phase 6 puts the AHJ first, not last.

Related Guides

• Complete Guide — conduit fill fundamentals and the NEC tables.
• Common Mistakes — the errors this checklist guards against.
• Code Compliance — the inspection checkpoints behind Phase 6.
• Estimating Guide — from checklist to material takeoff.
• Pro Tips — judgment calls for Phase 5.
• Conduit Size Calculator FAQ — quick answers to common questions.

Frequently Asked Questions

How long does the checklist take?

About five minutes per run once you’re familiar with it — against hours of rework when a skipped check fails inspection.

Do I need the checklist if I use the calculator?

Yes — the calculator is only as correct as its inputs. The checklist verifies the inputs (count, insulation, type) and the realities the calculator can’t see (bends, derating, permits).

What order do the phases run in?

Conductor list → derating → conduit size → route/pull plan → judgment → compliance. Each phase feeds the next; the order itself prevents the classic sequencing errors.

Should I document the checklist for the inspector?

Showing your fill math and bend tally at inspection time resolves most questions on the spot. A filled-out checklist is cheap credibility.

Does the checklist replace knowing the code?

No — it’s a verification tool, not an education. If any checkbox confuses you, that’s a signal to study the underlying rule (or call a licensed electrician), not to check the box anyway.

Get Your Number

Print this page, or keep it open next to the calculator: run your conductor list through the Conduit Size Calculator, then walk the six phases before you buy or pull. Five minutes of verification beats five hours of rework — every time.

Disclaimer: Calculator results are planning estimates based on your inputs and general NEC Chapter 9 fill tables; table values shown are approximate. This checklist is a planning aid, not a substitute for the current NEC, local amendments, or professional judgment. Electrical work is regulated — verify requirements with your local authority having jurisdiction (AHJ) and have the work performed or reviewed by a licensed electrician.