A framed wall connects two calculators that seem unrelated at first glance. The stud spacing calculator counts the vertical members the wall needs. The voltage drop worksheet estimates the voltage drop for a circuit run — typically through that same framing. The site links them in both directions: the cable size page says to use the stud spacing calculator to plan where cable runs through wall framing, and the stud spacing page says to use the cable size calculator to plan cable runs through the framed wall.
What each calculator does
The voltage drop worksheet takes voltage, current, one-way run length, and the candidate conductor’s resistance in ohms per 1,000 feet. For a two-conductor path, the voltage drop is 2 × current × resistance × one-way length ÷ 1,000, and the percentage drop divides that result by the system voltage. The page is explicit that it does not choose wire size, determine ampacity, or establish electrical-code compliance — you supply the conductor resistance from current manufacturer data, and the electrical work is designed and checked for the applicable installation.
The stud spacing calculator takes wall length, on-center spacing, and an explicit corner allowance. The geometric count is wall length divided by the spacing, rounded up, plus one end stud, plus the entered corner extras — for example, a 10-foot wall at 16 inches on center gives ceil(120 ÷ 16) = 8, plus one end stud and two corner extras for a count of 11. It also shows the first stud positions, but it does not recommend structural spacing, species, grade, load capacity, or wall suitability.
Side-by-side
| Voltage drop worksheet | Stud Spacing calculator | |
|---|---|---|
| Core question | What is the voltage drop for this run? | How many studs does this wall need? |
| Key inputs | Voltage, current, one-way length, conductor resistance | Wall length, on-center spacing, corner extras |
| Primary output | Voltage drop and percentage drop | Stud count, first positions, and corner allowance |
| Method | 2 × I × R × L ÷ 1,000, divided by system voltage | Ceiling(length ÷ spacing) + 1 end stud + corner extras |
| Design authority | Worksheet only — no wire sizing or ampacity | Count only — no structural spacing or load capacity |
| Code role | Adopted codes control safety-critical sizing | Framing plan needed for openings and load path |
When to use which
Use the stud spacing calculator when you are framing a wall and need the stud count and first positions for a layout — the count is a planning value that depends on the spacing and corner allowance you bring from your framing plan.
Use the voltage drop worksheet when you are checking a circuit run and want to see the voltage-drop arithmetic for a candidate conductor: enter the current, the one-way run length, and the conductor’s resistance per 1,000 feet from manufacturer data. The result is an estimate for comparison, and the page directs the actual wire sizing, ampacity, and code compliance to qualified design.
For the area of the wall or room behind either estimate, both pages point to the square footage calculator; for a deck with the same on-center layout, the stud spacing page points to the deck material calculator; and for elevated installation work on the cable side, to the ladder safety calculator.
Limits and disclaimer
Both calculators are planning worksheets, not design approvals. The cable size result depends entirely on the conductor resistance you enter and covers the voltage-drop check only — it does not select wire size, determine ampacity, or establish compliance with the National Electrical Code. The stud spacing result depends on the spacing and corner allowance you enter, and openings, intersections, backing, load path, species and grade, wall height, and adopted-code rules are not inferred. Qualified trades and adopted codes control safety-critical work.