--- title: "Wire Size for a 100 Amp Service: Copper, Aluminum | FigureYard" description: "Service wire for a 100 amp house: 4 AWG copper or 2 AWG aluminum under NEC Table 310.12, with a check for long runs to the meter." url: https://figureyard.com/energy/wire-size-for-100-amp-service/ image: https://figureyard.com/og/energy/wire-size-for-100-amp-service.png --- [Electrical, Heating & Insulation](https://figureyard.com/energy/) # Wire Size for a 100 Amp Service The service conductors for a 100 amp single-family house can be 4 AWG copper or 2 AWG aluminum. The code allows them to carry 83 percent of the service rating, because a home never draws its whole service at once, so they are a size smaller than a feeder of the same rating. That allowance covers only the conductors that carry the entire load of one dwelling. Reviewed by FigureYard editorial team · Updated October 13, 2026 · 7 sources *Interactive calculator on the page (inputs: The wire feeds; Load current; Circuit voltage; One-way distance; Conductor; Wire type; Runs for 3 hours or more at a time; Circuit; Allowed voltage drop (%)). The results below are for its default inputs.* **Wire size** **4 AWG** copper - Current the service wire must carry: **83.0** A - Rated for: **85** A - Voltage drop: **1.03** % - Longest run within 3%: **117** ft Each copper size for this circuit | Size | Rated | Drop | Fits | | --- | --- | --- | --- | | 10 AWG | 30 A | 4.13% | Too small for the current | | 8 AWG | 50 A | 2.59% | Too small for the current | | 6 AWG | 65 A | 1.64% | Too small for the current | | 4 AWG | 85 A | 1.03% | Yes | | 3 AWG | 100 A | 0.82% | Yes | | 2 AWG | 115 A | 0.65% | Yes | The calculator is set to a whole-house service at 100 amps and 240 volts. Enter the distance from the meter to the panel and choose the metal to see the size, and whether a long run calls for more. ## How to use this calculator 1. Leave the rating at 100 amps, the main breaker of the house. 2. Choose copper or aluminum. Most new services use aluminum SE or USE cable. 3. Enter the one-way distance from the meter or the service disconnect to the main panel. 4. For a subpanel or a detached building, switch to a circuit or a subpanel: the service allowance does not apply there. ## Worked examples ### A meter on the outside wall, panel just inside The wire feeds: A whole house (service) · Load current: 100 A · Circuit voltage: 240 V · One-way distance: 15 ft · Conductor: Aluminum - Wire size: 2 AWG aluminum - Current the service wire must carry: 83.0 A - Rated for: 90 A - Voltage drop: 0.40% - Longest run within 3%: 113 ft ### A meter on a pole at the edge of the lot The wire feeds: A whole house (service) · Load current: 100 A · Circuit voltage: 240 V · One-way distance: 140 ft · Conductor: Aluminum - Wire size: 1 AWG aluminum - Current the service wire must carry: 83.0 A - Rated for: 100 A - Voltage drop: 2.95% - Longest run within 3%: 142 ft ### A copper service in an older house The wire feeds: A whole house (service) · Load current: 100 A · Circuit voltage: 240 V · One-way distance: 30 ft - Wire size: 4 AWG copper - Current the service wire must carry: 83.0 A - Rated for: 85 A - Voltage drop: 0.77% - Longest run within 3%: 117 ft ## Service conductor size for a 100 amp dwelling by distance | One-way distance | Copper | Aluminum | | --- | --- | --- | | 25 ft | 4 AWG | 2 AWG | | 50 ft | 4 AWG | 2 AWG | | 100 ft | 4 AWG | 2 AWG | | 150 ft | 2 AWG | 1/0 AWG | | 200 ft | 1 AWG | 2/0 AWG | Each cell: the smallest conductor under the dwelling service rule that also keeps the drop at full rated current within the branch-circuit limit. ## The dwelling service rule NEC Table 310.12 lists the service sizes for one-family homes, and the rule behind it is simple: the conductors must carry 83 percent of the rating. For a service of 100 amps the table gives 4 AWG copper, rated 85 amps, or 2 AWG aluminum, rated 90 amps. It applies to the service entrance conductors and to the main feeder that carries the whole house's load, single-phase, without heat or bundling corrections. ## When the allowance does not apply A feeder to a subpanel, a detached garage or one wing of the house is sized from the regular ampacity table at the full rating: see the [100 amp subpanel](https://figureyard.com/energy/wire-size-for-100-amp-subpanel/) page, where the answer is 3 AWG copper or 1 AWG aluminum. A duplex served by one set of conductors, a three-phase service and a hot attic run all fall outside the rule too. ## Upgrading from a 100 amp service Many older homes have exactly this service. A heat pump, a car charger or an electric range can push the load past it, and the usual step up is a 200 amp service with new service conductors, meter base and panel, arranged with the utility. A load calculation by an electrician tells you whether the upgrade is needed; the [amps calculator](https://figureyard.com/energy/amp-calculator/) helps total up the big appliances first. ## Common questions ### What size wire for a 100 amp service? 4 AWG copper or 2 AWG aluminum for the service of a single-family house, under NEC Table 310.12, which sizes the conductors for 83 percent of the rating. ### Is 2 AWG aluminum good for 100 amp service? Yes, for a whole-house service: it is rated 90 amps, above the share of the rating the dwelling rule asks for. For a 100 amp subpanel it is too small; that needs 1 AWG aluminum. ### Can I use 4 AWG copper for 100 amps? For the service of a single-family house, yes. For any other 100 amp feeder, no: 4 AWG copper is rated 85 amps and the feeder must carry the full hundred. ### Does the distance to the meter change the size? On a long run, yes. With a meter on a pole far from the house, voltage drop can call for a larger size; enter the distance above to check. ## Related calculators - [Wire Size Calculator](https://figureyard.com/energy/wire-size-calculator/) - [Wire Size for a 200 Amp Service](https://figureyard.com/energy/wire-size-for-200-amp-service/) - [Wire Size for a 100 Amp Subpanel](https://figureyard.com/energy/wire-size-for-100-amp-subpanel/) - [Voltage Drop Calculator](https://figureyard.com/energy/voltage-drop-calculator/) - [Amp Calculator](https://figureyard.com/energy/amp-calculator/) Reviewed by FigureYard editorial team on 2026-10-13. Formulas are tested against published values, and material figures come from the sources below. [How we build our calculators](https://figureyard.com/editorial-policy/). ## Sources - [Michigan State University Electrical Tech Note 227: Sizing Conductors to Minimize Voltage Drop (Table 227.1, dc resistance at 75 °C)](https://www.maec.msu.edu/download_file/view/147/303) - [Cerrowire Voltage Drop Table (rev. 09/2018)](https://www.cerrowire.com/wp-content/uploads/2018/09/Cerrowire_Voltage-Drop_210521.pdf) - [Electrical License Renewal (reproduces NEC 210.19(A)(1) text): 210.19(A)(1) Branch Circuits.](https://www.electricallicenserenewal.com/Electrical-Continuing-Education-Courses/NEC-Content.php?sectionID=818) - [Encore Wire (Prysmian): Wire Ampacity Size Table](https://www.encorewire.com/products/tools-and-resources/calculators/wire-size-table.html) - [City and County of Denver (Denver Residential Code 2021, adopting the 2021 IRC); viewer hosted by UpCodes: Chapter 36 Services: Denver Residential Code 2021 (based on the 2021 International Residential Code), Section E3603.1.1 Ungrounded Service Conductors](https://up.codes/viewer/denver/irc-2021/chapter/36/services) - [Cerrowire Ampacity Chart (ampacities based on the 2017 NEC Table 310.16)](https://www.cerrowire.com/wp-content/uploads/2021/04/Cerrowire_Ampacity_Chart_210405.pdf) - [Mesa County (Colorado) Community Development Department, Building Division: Homeowner's Wiring Guideline 2020 (Administrative Review Application Process), effective March 1, 2021](https://www.mesacounty.us/sites/default/files/2022-12/residential-wiring-guideline-2020-nec-effective-3-1-2021.pdf)