About BoxFillCalculator.com
The most trusted free box fill calculator for electricians, contractors, and inspectors.
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. That's why 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.
Accuracy Verified
All calculations are verified against NEC Table 314.16(A) and Table 314.16(B) values. We apply the same rules inspectors use.
Built by Professionals
Our team includes licensed electricians and electrical engineers who understand real-world installation challenges.
Always Free
No subscriptions, no premium tiers, no hidden costs. Our calculator is completely free to use—no email required.
Our Expertise
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:
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 a licensed electrician or your local authority having jurisdiction (AHJ) for final approval. Local codes may have additional requirements beyond the NEC.
Ready to Calculate?
Try our free box fill calculator and see why thousands of electricians trust BoxFillCalculator.com.
Open Box Fill Calculator