Savings calculator
What sizing each run for voltage drop saves on copper.
Most crews upsize by habit. That buys copper some runs don't need and misses the runs that do. Pick a job like yours and change anything.
- Runs sized down
- 12 of 40
- Runs your rule missed
- None
- Padding not bought
- 1,179 ft
#12 stays within 3% out to 142 ft at 16 A and 277 V. #10 reaches 234 ft. Estimated with NEC 2023 Chapter 9, Table 9 impedance at 0.9 power factor; ZapSketch measures each run from the plan.
Show the math
Same voltage-drop method as the app, for one single-phase run in EMT:
VD% = 2 × L × I × Z ÷ 1000 ÷ V × 100
Z = R × PF + X × sin(acos PF)
- L
- one-way run length in feet
- I
- 16 A design load
- V
- 277 V
- R, X
- NEC Chapter 9 Table 9, uncoated copper, steel conduit column
- PF
- 0.9, the app's default power factor. #12 Z = 1.830, #10 Z = 1.107, #8 Z = 0.730 Ω per 1000 ft
Each run gets the smallest size that is at least the breaker's minimum and keeps voltage drop at or under the target. The rule of thumb picks its size without checking voltage drop. Both buy three conductors per run, with the equipment ground upsized along with the circuit conductors (250.122(B)).
Cost = 3 × length × price per foot. The rule of thumb buys the length plus padding; sized runs buy the measured length. Run lengths spread from 35% to 165% of the average.
What the app does that this page doesn't
- Ampacity. Here the minimum size comes from the breaker. The app checks Table 310.16 with the terminal temperature rating, ambient temperature correction, adjustment for more than three current-carrying conductors, continuous load at 125%, and 240.4(D).
- Length. Here lengths are spread around an average. The app measures each run along its drawn route through every box to each device, adds vertical rise and drop from your elevation settings, and checks the longest path on the circuit.
- Raceway and power factor. Here every run is EMT at 0.9. The app uses each segment's raceway type (EMT or PVC) and each circuit's power factor.
- Circuit types. Here every circuit is single-phase. The app uses √3 for three-phase circuits and Table 8 resistance for DC.
- Equipment ground and fill. Here the ground matches the circuit conductors. The app sizes it from Table 250.122 with proportional upsizing, and checks conduit fill for every raceway, including the grounds.
- Precision. The app uses exact decimal math and shows the inputs behind every result.
How it works
Measure the plan, draw home runs, export the pull schedule and estimate.
Start with whatever you have
Import a plan PDF and measure one known dimension. No plan? Sketch the walls and rooms by typing lengths. Or skip both: draw freeform on a blank sheet and type in the run lengths you know.
Draw your home runs
Place panels, boxes and devices, then draw the raceways. Every run is measured and sized as you go.
Check, price and hand off
Review drop, size and fill per run. Price the job from the same drawing, then export the marked-up plan, the pull schedule and a customer proposal.
Who it's for
Commercial
Commercial takeoff and pull schedules
Measure every run from the drawing and size it once. The estimator bids from the same numbers the foreman pulls from.
- Home runs from every panel on the sheet
- 277 V lighting and 120 V receptacles sized run by run
- Conduit fill checked where runs share a raceway
| Run | From → To | Circuit | Length | Conductors | Raceway | Fill | VD |
|---|---|---|---|---|---|---|---|
| R1 | LP-1 → JB-3 | LP1-1, 3, 5 | 64 ft | 6 #12, 3 #10 | 3/4" EMT | 27% | — |
| R1A | JB-3 → D-12 | LP1-5 | 88 ft | 3 #10 | 1/2" EMT | 21% | 2.20% |
| R1B | JB-3 → D-7 | LP1-1 | 37 ft | 3 #12 | 1/2" EMT | 13% | 2.56% |
| R2 | LP-1 → D-15 | LP1-7 | 41 ft | 3 #12 | 1/2" EMT | 13% | 1.08% |
| R3 | LP-1 → D-20 | LP1-9 | 117 ft | 3 #12 | 1/2" EMT | 13% | 2.68% |
Example pull schedule: 20 A lighting circuits at 277 V, 16 A design load, 3% target. Calculated from NEC 2023 tables.
Residential
Residential estimates from a room sketch
Most houses don't come with a plan. Draw the room in a minute, drop in the devices, and turn it into a material list and a price you can quote.
- Walls and rooms from typed lengths like 14'6"
- GFCI, receptacles, switches and fixtures where they go
- Material list, labor and a customer proposal from the sketch
1 · Sketch the room
Type the wall lengths. The sketch sets the scale.
2 · Place devices
Three GFCIs on the counter, the range and the dishwasher.
3 · Price it Free during beta
A material list and labor from what's on the sketch, at your prices.
Free
Plan, measure and size every run. Estimating is free during beta. Exports carry a watermark.
Start free