What it calculates
Estimate branch-circuit cable length with waste.
Romex / NM-B Length Calculator
Estimate NM-B cable needed from branch-circuit runs, drops and waste allowance.
Planning and estimating aid only. Verify project requirements, manufacturer instructions, adopted codes, permits, and field conditions before performing regulated work.
Electrical planning
How to Use This Calculator
Enter the measurements and job information you know, select Calculate, then use the result as a starting point for estimating, purchasing or project planning.
How the calculation works
Base cable = number of runs × (average run + routing/drop allowance). The waste/slack percentage is then added.
What the result means
Measure real routing paths whenever possible; straight-line room dimensions often understate cable needed.
Use real project measurements
Start with the actual field dimensions or equipment values from the job. Run the calculator once with your measured quantity, then test a second scenario with your normal waste, routing or safety allowance. This makes the tool useful for both the takeoff and the customer estimate.
Contractor tip: Save the measurements that produced your estimate in the job notes so the quantity can be checked later if the scope changes.
Verify the final quantity
Use the result as an estimating and layout aid. Final conductor, breaker, service, raceway and equipment selections must be checked against the adopted electrical code, equipment listings and local requirements.
Good practice: Compare the calculated quantity with plans, specifications, product packaging and current field conditions before purchasing material.