Electrical calculators.
16 free calculators for electricians, apprentices, and exam prep. They run in your browser, show every step, and name the 2026 NEC sections they used, so you can check the work in your own code book.
Sizing and code calculators
Each result lists the steps and the NEC 2026 sections it applied.
- Voltage dropVolts lost and percent drop on a copper or aluminum run, single- or three-phase.210.19 and 215.4 informational notes
- Box fillMinimum box volume from conductors, devices, clamps, and grounds.314.16(B), Table 314.16(B)(4)
- Conduit fillSmallest EMT, IMC, RMC, or PVC that fits your conductors.Chapter 9 Table 1, Annex C
- Ampacity deratingApply ambient temperature and bundling adjustments to a conductor.310.15(B) and 310.15(C)(1)
- Ground wire (EGC) sizeMinimum equipment grounding conductor from the breaker or fuse size.250.122, Table 250.122
- Grounding electrode conductorGEC size from the service conductors, with ground rod and Ufer limits.250.66, Table 250.66
- Residential service loadStandard-method dwelling load calculation, with EV charger.Article 120 (moved from 220 in 2026)
- Motor branch circuitConductor ampacity, breaker or fuse size, and feeder for motors.430.22, 430.24, 430.52
- Motor overloadMaximum overload setting from nameplate current and service factor.430.32(A)(1), 430.32(C)
- Transformer protectionMaximum primary and secondary breaker or fuse for a transformer.450.5 (was 450.3)
- Tap rulesCheck 10 ft, 25 ft, and transformer secondary taps.240.21(B) and 240.21(C)(6)
- Solar PV and 120% rulePV circuit current, conductor and fuse minimums, and the busbar 120% rule.690.8, 690.9, 705.12(B)(2)
Conduit bending calculators
Mark spacing, shrink, and take-up for EMT. Trade math, not code rules.
- Offset bendDistance between bends and shrink for any offset.Trade math
- 90° stub-upWhere to mark the EMT for a stub at the height you need.Trade math
- 3-point saddleCenter and outer marks to cross a pipe or obstruction.Trade math
- 4-point saddleFour marks to cross a wide obstruction like a duct or beam.Trade math
Conduit bending cheat sheet: multipliers, shrink, take-up, and saddle marks on one page.
Questions about the calculators
Are the Ask Shorty electrical calculators free?
Yes. All of them are free, with no sign-up. They run in your browser, show every step, and name the 2026 NEC sections they used so you can check the work in your own code book.
Which calculator do I use to size a circuit?
Use the voltage drop calculator for wire length and load, the ampacity derating calculator for hot conditions or many conductors in one raceway, and the ground wire calculator for the equipment grounding conductor. For service sizing, use the residential service load calculator.
Which calculator do I use for boxes and conduit?
Use the box fill calculator to count conductors, devices, and fittings against box volume. Use the conduit fill calculator to check how many conductors fit in a raceway.
Which calculators help with conduit bending?
The offset bend, 90 degree stub-up, 3-point saddle, and 4-point saddle calculators give mark spacing, shrink, and take-up for EMT. The conduit bending cheat sheet puts the multipliers on one page.
I teach electrical students. How do I use these in class?
Send students to the calculators to check their work, then use the Ask Shorty lesson builder to make a cited slide deck and quiz on any NEC topic, in the order you teach it. The builder is in a free pilot, so you request a code first.
Teaching a class? Build a lesson and quiz on any NEC topic.