About BoxFillCalculator.com
A free NEC 314.16 box fill calculator with a full itemized volume breakdown for compliant installations.
Our Mission
BoxFillCalculator.com was created with a simple goal: provide electricians with a free, accurate, and easy-to-use tool for calculating electrical box fill per NEC 314.16.
We believe that code compliance tools should be accessible to everyone -- from apprentice electricians learning the trade to master electricians verifying complex installations. Our calculator is 100% free, requires no registration, and works on any device.
Why Trust Our Calculator?
NEC 2023 Compliant
Our calculator is updated for the latest National Electrical Code, including the new 314.16(B)(6) terminal block requirements.
Based on NEC Tables
Volumes use the values in NEC Table 314.16(A) and conductor allowances use Table 314.16(B). Always confirm the final layout against the adopted code and local amendments.
Mapped to the Code
Every allowance in this tool maps to a specific NEC 314.16 rule — conductor, device, clamp, grounding, support fitting, and terminal block — so you can check each line against the code.
Always Free
No subscriptions, no premium tiers, no hidden costs. Our calculator is completely free to use -- no email required.
Topics Covered
BoxFillCalculator.com specializes in NEC 314.16 box fill requirements. Our knowledge base covers:
Conductor Volume
NEC Table 314.16(B) allowances
Device Fill
314.16(B)(4) requirements
Grounding
314.16(B)(5) calculations
Clamp Fill
Internal vs external clamps
Terminal Blocks
NEC 2023 314.16(B)(6)
Box Sizing
NEC Table 314.16(A)
Educational Resources
Beyond our calculator, we provide comprehensive guides to help you understand NEC box fill requirements:
Complete NEC 314.16 Guide
Everything you need to know about box fill
Step-by-Step Calculations
Learn to calculate box fill manually
Common Mistakes
Avoid the top 10 calculation errors
NEC Code Reference
Quick lookup for 314.16 sections
Important Disclaimer
BoxFillCalculator.com is provided as a reference tool to assist with NEC 314.16 calculations. While we strive for accuracy, this calculator should not be the sole basis for electrical design decisions. Always verify calculations manually and consult with an electrician or your local authority having jurisdiction (AHJ) for final approval. Local codes may have additional requirements beyond the NEC.
Ready to Calculate?
Calculate electrical box fill per NEC 314.16 with a clear, itemized volume breakdown.
Open Box Fill Calculator