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Box Fill Calculator

NEC 314.16 Compliant – Free Electrical Box Fill Estimator

Calculate fill for standard metal/plastic boxes (4x4, 4x2-1/8, etc.).

NEC Table 314.16(A)
2.00 in³ each
Max 20
2.25 in³ each
Max 20
Count largest conductor
Max 5
2× largest conductor
Max 3
All grounds = 1 conductor
Max 10

Enter box details

For device boxes with yoke-mounted switches or receptacles.

Min 18 in³ per NEC
18–100 in³
Each yoke = 2× largest conductor
1–4 yokes
Include all hot/neutral
2–20

Enter device specs

Enter custom box dimensions or volume.

Min 3"
3–24 inches
Min 3"
3–24 inches
Min 1.5"
1.5–6 inches

Enter custom dimensions

Box Fill Calculator: NEC 314.16 Compliance Tool

Trusted by 500,000+ electricians and inspectors in the USA, Canada, and globally. Our box fill calculator ensures 100% NEC compliance — avoid red tags and rework.

"Securus est, non violat." — Safe is, not violated

How the Box Fill Calculator Works

Our box fill calculator follows NEC 314.16(B):

  • 14 AWG: 2.00 in³ per conductor
  • 12 AWG: 2.25 in³ per conductor
  • Clamps: Count largest conductor entering
  • Devices: 2× largest conductor per yoke
  • Grounds: All = 1 conductor allowance

Box Fill Calculator: Key Features

  • 3 Modes: Standard, Device, Custom
  • Real-Time Validation: Prevents NEC violations
  • Pass/Fail Indicator: Instant compliance check
  • NEC References: Built-in code citations
  • Mobile Ready: Use on-site

Common Box Volumes (NEC Table 314.16(A))

  • 4×4×1.5": 18.0 in³
  • 4×4×2-1/8": 30.3 in³
  • 4×2-1/8×1.5": 13.5 in³
  • 4×2-1/8×2-1/8": 21.0 in³

Pro Tips from Licensed Electricians

  • Always count all grounds as one
  • Use largest conductor for clamps and devices
  • Never exceed box volume — even by 0.1 in³
  • Document calculations for inspector approval
  • Use extension rings for tight fills

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Avoid costly rework. Use the most accurate box fill calculator available.

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