Electrical Room Sizing Calculator

How This Works

This calculator applies NEC 110.26 requirements for working space around electrical equipment. It determines minimum room dimensions based on:

• Working clearance depth (NEC 110.26(A)(1)) — front clearance based on voltage and condition (1, 2, or 3)
• Working clearance width (NEC 110.26(A)(2)) — 30" minimum or equipment width, whichever is greater
• Headroom (NEC 110.26(A)(3)) — 6'-6" minimum or equipment height, whichever is greater
• Dedicated equipment space (NEC 110.26(E)) — width and depth of equipment extending from floor to 6' above or structural ceiling
• Entrance/egress (NEC 110.26(C)) — at least one entrance not less than 24" wide x 6'-6" high; two entrances required for large equipment (rated 1200A+ or 6'+ wide) when the room depth exceeds the required working clearance

2023 NEC Updates: NEC 110.26(A)(4) now requires clearance for equipment doors in the open position. Working space cannot be impeded by open doors to less than the required width. This calculator accounts for swinging panel doors.

Voltage scope: NEC 110.26 applies to equipment rated 1000V nominal or less. For equipment over 1000V (medium voltage switchgear, unit substations), working clearances are governed by NEC 110.34 and Table 110.34(A), which have different and generally larger clearance requirements. This calculator covers 110.26 only. The 601-1000V row was added to NEC Table 110.26(A)(1) in the 2017 cycle — values in this range should be verified with your Authority Having Jurisdiction (AHJ).

Sources: NFPA 70 National Electrical Code 2023 Edition, Article 110.26. Equipment dimensions are typical manufacturer sizes — verify with actual submittals.

Disclaimer: This tool provides minimum code-compliant dimensions. Actual room sizing should account for maintenance access, future expansion, ventilation requirements, and local amendments to the NEC. Always verify with the AHJ (Authority Having Jurisdiction).

Code Edition Notice: Clearance values are from NEC 2023 (NFPA 70), Table 110.26(A)(1). The NEC updates every 3 years — the 2026 edition has been published. State adoption varies widely: as of early 2026, DE/NJ/CT enforce NEC 2020; PA enforces NEC 2017. The 601-1000V row was added in the 2017 cycle and may not be recognized in all jurisdictions. For equipment over 1000V, NEC 110.34 applies (not covered here). Always confirm which NEC edition your AHJ has adopted before using these clearances for design.