# Conduit Fill API > NEC conduit-fill and box-fill maths as an API, computed locally and deterministically — the electrical-code calculations an electrician or estimator does on every run. The conduit-fill endpoint takes a set of conductors (as size:count pairs, e.g. 12:3,10:2) and a conduit trade size and returns the conductor cross-sectional area, the conduit's internal area, the fill percentage and whether it stays within the NEC Chapter 9 limit — 53 % for a single conductor, 31 % for two, 40 % for three or more — so nine #12 THHN fill a half-inch EMT to 39 % (legal) but ten do not. The box-fill endpoint applies NEC 314.16(B): each conductor adds its free-space allowance (2.00 in³ for #14, 2.25 for #12, and so on), a device yoke counts as two, internal cable clamps as one, and all equipment grounds together as one — all at the largest conductor's volume — to give the minimum junction-box size, checked against a box volume if you give one. Uses the THHN/THWN and EMT areas from NEC Chapter 9. Everything is computed locally and deterministically, so it is instant and private. Ideal for electrical-contractor, estimating, inspection and electrician app developers, conduit and box-sizing tools, and apprentice training. Pure local computation — no key, no third-party service, instant. Imperial: square inches and cubic inches. Live, nothing stored. 2 compute endpoints. Always verify against the adopted code edition — this is an estimating aid, not an inspection. ## Authentication All requests require your oanor API key in the `x-oanor-key` header. Get one at https://www.oanor.com/developer/keys. ```bash curl -H "x-oanor-key: oanor_live_…" "https://api.oanor.com/conduit-api/..." ``` ## Pricing - **Free** (Free) — 4,950 calls/Mo, 2 req/s - **Starter** ($5/Mo) — 49,000 calls/Mo, 6 req/s - **Pro** ($14/Mo) — 214,000 calls/Mo, 15 req/s - **Mega** ($44/Mo) — 1,285,000 calls/Mo, 40 req/s ## Endpoints ### Conduit #### `GET /v1/box-fill` — NEC 314.16 box fill **Parameters:** - `conductors` (query, optional, string) — size:count pairs, e.g. 14:3 Example: `14:3` - `wire_size` (query, optional, string) — Single wire size Example: `14` - `count` (query, optional, string) — Count for single size Example: `3` - `devices` (query, optional, string) — Device yokes (receptacles/switches) Example: `1` - `clamps` (query, optional, string) — Internal cable clamps present Example: `true` - `grounds` (query, optional, string) — Equipment grounds present Example: `1` - `box_volume` (query, optional, string) — Box volume to check (in³) **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/conduit-api/v1/box-fill?conductors=14%3A3&wire_size=14&count=3&devices=1&clamps=true&grounds=1" ``` **Response:** ```json { "data": { "note": "NEC 314.16(B): each conductor adds its free-space allowance; a device counts as 2×, internal clamps as 1×, and all equipment grounds together as 1× — all at the largest conductor's volume.", "inputs": { "clamps": 1, "devices": 1, "conductors": [ { "size": "14", "count": 3 } ], "ground_systems": 1 }, "required_volume": 14, "volume_breakdown": { "clamps": 2, "devices": 4, "grounds": 2, "conductors": 6 } }, "meta": { "timestamp": "2026-06-05T21:48:45.876Z", "request_id": "602decef-b32e-436a-aaa7-d27d98ea72d5" }, "status": "ok", "message": "Box fill", "success": true } ``` #### `GET /v1/conduit-fill` — NEC conduit fill % **Parameters:** - `conductors` (query, optional, string) — size:count pairs, e.g. 12:3,10:2 Example: `12:3,10:2` - `wire_size` (query, optional, string) — Single wire size (AWG/kcmil) Example: `12` - `count` (query, optional, string) — Count for single size Example: `3` - `trade_size` (query, optional, string) — EMT trade size (1/2, 3/4, 1, …) Example: `1/2` - `conduit_area` (query, optional, string) — Override conduit area (in²) **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/conduit-api/v1/conduit-fill?conductors=12%3A3%2C10%3A2&wire_size=12&count=3&trade_size=1%2F2" ``` **Response:** ```json { "data": { "note": "NEC Chapter 9: max fill is 53% for 1 conductor, 31% for 2, 40% for 3 or more. Fill % = conductor area / conduit area; it must stay within the allowable.", "inputs": { "conductors": [ { "size": "12", "count": 3 }, { "size": "10", "count": 2 } ], "trade_size": "1/2", "conduit_area": 0.304 }, "spare_area": 0.0395, "fill_percent": 27.0066, "within_limit": true, "allowable_area": 0.1216, "conductor_area": 0.0821, "conductor_count": 5, "max_fill_percent": 40 }, "meta": { "timestamp": "2026-06-05T21:48:45.953Z", "request_id": "645c4d96-6761-4479-b03c-10b329382c97" }, "status": "ok", "message": "Conduit fill", "success": true } ``` ### Meta #### `GET /v1/meta` — Spec **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/conduit-api/v1/meta" ``` **Response:** ```json { "data": { "notes": "THHN/THWN conductor and EMT areas (NEC Chapter 9); box-fill volumes (NEC 314.16(B)). Conductors as 'size:count' pairs (e.g. 12:3,10:2). Imperial: in² and in³. Verify against the current code; this is an estimating aid.", "service": "conduit-api", "endpoints": { "GET /v1/meta": "This document.", "GET /v1/box-fill": "Required junction-box volume (NEC 314.16) from conductors, devices, clamps and grounds.", "GET /v1/conduit-fill": "Conduit fill % and pass/fail (NEC Chapter 9) for a set of conductors in EMT." }, "description": "NEC conduit fill and box fill for electricians: conductor area vs conduit capacity, and junction-box volume requirements." }, "meta": { "timestamp": "2026-06-05T21:48:46.011Z", "request_id": "d06f22fe-6213-428e-bf64-8d75f57f5f45" }, "status": "ok", "message": "Meta", "success": true } ``` --- Marketplace page: https://www.oanor.com/api/conduit-api OpenAPI spec: https://www.oanor.com/api/conduit-api/openapi.json