Guide · Updated 14/08/2026
Conduit Pipe Size Chart for Electrical Wiring in India
Electricians ask us the same three questions at the counter: which size, which grade, and how many wires will fit. This chart answers all three — with the same numbers we run on the extrusion line at Pirana.
1. Sizes, walls and inside diameters
Conduit is sold by nominal outside diameter (OD). Wall thickness depends on grade — LMS (light), MMS (medium), HMS (heavy) — and the wall is what you're paying for: it decides crush resistance during slab casting. Inside diameter (ID) is simply OD minus two walls, and ID is what limits how many wires fit.
| Nominal OD | Grade | Wall | Approx. ID | Typical use |
|---|---|---|---|---|
| 19 mm | LMS / MMS / HMS | 1.2 / 1.5 / 2.0 mm | 16.6 / 16.0 / 15.0 mm | Light & surface runs, point wiring |
| 20 mm | LMS / MMS / HMS | 1.5 / 2.0 / 2.1 mm | 17.0 / 16.0 / 15.8 mm | Standard concealed circuits |
| 25 mm | LMS / MMS / HMS | 1.5 / 2.0 / 2.1 mm | 22.0 / 21.0 / 20.8 mm | Mains runs, DB feeds, bunched circuits |
| 32 mm | LMS / MMS / HMS | 1.5 / 2.0 / 2.1 mm | 29.0 / 28.0 / 27.8 mm | Feeders, risers, multi-circuit pulls |
2. How many wires fit? (40% fill rule)
Fill a conduit past ~40% of its internal area and wires start scuffing on the pull and running hot in service. Using that rule with common FR-insulated copper wire ODs (≈2.8 mm for 1.5 sq mm, ≈3.2 mm for 2.5 sq mm), the practical counts are:
| Conduit (MMS) | 1.5 sq mm wires | 2.5 sq mm wires |
|---|---|---|
| 19 mm | 10–12 | 8–10 |
| 20 mm | 10–12 | 8–10 |
| 25 mm | 17–20 | 13–16 |
| 32 mm | 30+ | 24+ |
3. Which grade for which job
LMS — surface runs, false-ceiling feeds, light duty. MMS — the default for concealed wall chases in brickwork. HMS — anywhere conduit is cast into RCC: slabs, columns, beams, or where trolleys and rebar walk over it before the pour. The extra wall is cheap insurance against a crushed run you can never re-pull.
On 20mm and 25mm, our LMS and MMS grades carry the ISI mark under IS 9537 (Part 3), licence CM/L-7200284611 — printed on the pipe, verifiable on the BIS portal. Full details on the ISI quality page.
Published trade rates, bundle packing, same-day Ahmedabad dispatch — full price list here.