# SparkQuote

> Free NEC calculators and an AI estimator for electrical contractors: upload the plans, review the counts, send the proposal.

SparkQuote is an AI estimator for electrical contractors in the United States: it does the takeoff from PDF plans, applies the contractor's labor units and prices, and builds the proposal. The estimator is open as a free beta at https://app.sparkquote.ai (5 AI takeoffs a month, no credit card): AI takeoff from PDF plans with review on the plan, click-to-count, find-all-like-this, scale and measurement, a labor-unit library, estimates, Excel export and a PDF proposal. Features the product pages mark as planned are not live yet, and the paid plans on /pricing start after the beta.

The calculators and reference charts are free, need no sign-up, and follow the NEC 2023 (NFPA 70). Each calculator shows its formula, the NEC table or section it uses, and a worked example. The method and test cases are described at https://sparkquote.ai/about/how-we-build-our-calculators.

The same calculators are available to AI assistants as a remote MCP server (Streamable HTTP, no sign-in): https://sparkquote.ai/mcp. It offers the nine calculators plus a Table 310.16 ampacity lookup; every result names the NEC table used and links the calculator page.

Results are code minimums under stated assumptions. Local amendments and the edition a jurisdiction has adopted can change the answer; the inspector has the final say.

Full text of every page: https://sparkquote.ai/llms-full.txt

## Free electrical calculators

- [Free Electrical Calculators](https://sparkquote.ai/tools): Free electrical calculators for electricians: voltage drop, wire size, conduit fill, box fill, load calculation, watts to amps, Ohm's law and bid pricing.
- [Box Fill Calculator](https://sparkquote.ai/tools/box-fill-calculator): Free NEC 314.16 box fill calculator: count conductors, devices, clamps and grounds the way an inspector does and get the minimum box volume in in³.
- [Conduit Fill Calculator](https://sparkquote.ai/tools/conduit-fill-calculator): Free conduit fill calculator using NEC Chapter 9 Tables 1, 4 and 5. Add conductors, pick EMT or PVC, and get percent fill and the smallest conduit that passes.
- [Electrical Bid Calculator](https://sparkquote.ai/tools/electrical-bid-calculator): Free electrical bid calculator: enter materials, labor hours, labor rate, overhead and margin to get the bid price, the break-even price and your profit.
- [Residential Electrical Load Calculator](https://sparkquote.ai/tools/electrical-load-calculator): Free NEC dwelling load calculator: enter square footage, appliances, HVAC and EV chargers to get the calculated load in VA, amps and the service size.
- [NEC Calculator MCP Server](https://sparkquote.ai/tools/mcp-server): Add SparkQuote's free NEC calculators to Claude, ChatGPT or any MCP client. Ten tools for wire size, ampacity, voltage drop, conduit fill and more, with no sign-in.
- [Ohm's Law Calculator](https://sparkquote.ai/tools/ohms-law-calculator): Enter any two values to solve for volts, amps, ohms and watts. Includes the Ohm's law wheel, all 12 formulas and field examples electricians use.
- [Panel Schedule Template and Generator](https://sparkquote.ai/tools/panel-schedule-template): Create a printable electrical panel schedule: enter circuits, breakers and loads and get a balanced, inspector-ready PDF or Excel file for 1- or 3-phase panels.
- [Voltage Drop Calculator](https://sparkquote.ai/tools/voltage-drop-calculator): Free voltage drop calculator for single- and three-phase circuits: enter amps, distance and wire size to get percent drop and the size that stays under 3%.
- [Watts to Amps Calculator](https://sparkquote.ai/tools/watts-to-amps): Convert watts to amps for 120 V, 240 V and three-phase circuits with power factor. Includes conversion charts and how to size the breaker and wire.
- [Wire Size Calculator](https://sparkquote.ai/tools/wire-size-calculator): Find the right wire size for any circuit: enter amps, distance, voltage and material to check NEC 310.16 ampacity, terminal ratings and voltage drop.

## Wire size by amperage

- [Wire Size by Amps](https://sparkquote.ai/wire-size): What size wire for every common breaker, from 15 to 200 amps, in copper and aluminum, with links to the full answer, distance tables and grounding for each.
- [What Size Wire for a 100 Amp Service?](https://sparkquote.ai/wire-size/100-amp-service): A 100 amp home service uses 4 AWG copper or 2 AWG aluminum (NEC Table 310.12). Ground wire size, conduit size and when the 83% rule doesn't apply.
- [What Size Wire for a 100 Amp Subpanel?](https://sparkquote.ai/wire-size/100-amp-subpanel): A 100 amp subpanel feeder needs 3 AWG copper or 1 AWG aluminum at 75°C plus an 8 AWG copper ground. Distance, conduit size and detached-building rules.
- [What Size Wire for 125 Amps?](https://sparkquote.ai/wire-size/125-amp): 125 amp wire size: 2 AWG copper or 1/0 aluminum for a dwelling service, 1 AWG copper or 2/0 aluminum for a subpanel feeder. Grounds, conduit and distance.
- [What Size Wire for a 15 Amp Circuit?](https://sparkquote.ai/wire-size/15-amp): A 15 amp circuit uses 14 AWG copper (14/2 NM-B) or 12 AWG aluminum. How far 14 gauge can run by load, which circuits suit 15 A, and when to use 12 AWG.
- [What Size Wire for 150 Amps?](https://sparkquote.ai/wire-size/150-amp): A 150 amp home service uses 1 AWG copper or 2/0 aluminum (Table 310.12); a 150 amp subpanel feeder needs 1/0 copper or 3/0 aluminum. Grounds, conduit, distance.
- [What Size Wire for a 20 Amp Circuit?](https://sparkquote.ai/wire-size/20-amp): A 20 amp circuit needs 12 AWG copper (12/2 NM-B) or 10 AWG aluminum. Why 14 gauge is never allowed, when to upsize for distance, and which circuits need 20 A.
- [What Size Wire for a 200 Amp Service?](https://sparkquote.ai/wire-size/200-amp-service): A 200 amp home service uses 2/0 copper or 4/0 aluminum (NEC Table 310.12). Ground wire sizes, conduit size, meter-main feeders and 200 A subpanel sizing.
- [What Size Wire for a 30 Amp Breaker?](https://sparkquote.ai/wire-size/30-amp): Use 10 AWG copper for a 30 amp breaker (10/2 or 10/3 NM-B), or 8 AWG aluminum. When to upsize for distance, plus dryer, water heater and RV examples.
- [What Size Wire for a 40 Amp Breaker?](https://sparkquote.ai/wire-size/40-amp): A 40 amp breaker needs 8 AWG copper in NM-B or THHN, or 8 AWG aluminum at 75°C (6 AWG at 60°C). Distance limits, conduit size, cooktop and EV examples.
- [What Size Wire for a 50 Amp Breaker?](https://sparkquote.ai/wire-size/50-amp): A 50 amp circuit needs 6 AWG copper in NM-B cable, or 8 AWG copper THHN in conduit with 75°C terminals. Aluminum, distance tables and range, EV and RV examples.
- [What Size Wire for a 60 Amp Breaker?](https://sparkquote.ai/wire-size/60-amp): For a 60 amp breaker use 6 AWG copper THHN with 75°C terminals, 4 AWG copper in 60°C cable, or 4 AWG aluminum. Subpanel, EV charger and heat strip examples.

## NEC reference charts

- [Wire Ampacity Chart and Wire Size Chart](https://sparkquote.ai/ampacity-chart): Copper and aluminum wire ampacity chart (NEC Table 310.16), a wire size chart by breaker, the 83% service table and the rules for which column to use.
- [Conduit Fill Chart for EMT and PVC](https://sparkquote.ai/conduit-fill-chart): How many wires fit in a conduit? Conduit fill charts for EMT and PVC Schedule 40 with THHN from 14 AWG to 4/0, computed from NEC Chapter 9 Tables 1, 4 and 5.
- [Electrical Symbols for Blueprints](https://sparkquote.ai/electrical-symbols): A practical chart of electrical blueprint symbols: receptacles, switches, lighting, panels, low voltage and fire alarm, plus how to read legends and schedules.
- [How to Calculate Voltage Drop](https://sparkquote.ai/voltage-drop-formula): The voltage drop formula for single- and three-phase circuits, the K-factor and impedance methods, and worked examples solving for wire size and distance.
- [Wire Gauge Chart (AWG)](https://sparkquote.ai/wire-gauge-chart): AWG wire gauge chart with diameter in inches and mm, circular mils, area and ampacity for 14 AWG to 4/0. Plus how to tell a wire's gauge in the field.
- [XHHW-2 Wire: Ratings, Ampacity and XHHW vs. THHN](https://sparkquote.ai/xhhw-wire): What XHHW-2 wire is, its 90°C wet and dry rating, an XHHW-2 ampacity chart for copper and aluminum (NEC Table 310.16), and how it compares with XHHW and THHN/THWN-2.

## Estimating, bidding and pricing guides

- [Electrical Estimating and Bidding Guides](https://sparkquote.ai/guides): Guides for electrical contractors: how to estimate and bid electrical work, NECA labor units, profit margins, hourly rates, and where to find jobs to bid.
- [Best AI Electrical Takeoff Software for 2026](https://sparkquote.ai/guides/best-ai-electrical-takeoff-software): The best AI electrical takeoff software for 2026: Drawer AI, Countfire, Accubid LiveCount, STACK, Togal.AI, BuildVision and more, with what each AI counts and costs.
- [Best Electrical Estimating Software for 2026](https://sparkquote.ai/guides/best-electrical-estimating-software): The 11 best electrical estimating software tools for 2026 for small shops, commercial bids and the cloud, with dated prices. We make SparkQuote; it isn't ranked.
- [Electrical Contractor Profit Margins: Benchmarks, Markup, and Where Profit Leaks](https://sparkquote.ai/guides/electrical-contractor-profit-margin): Average electrical contractor profit margins, gross vs. net margin, a margin-to-markup table, overhead math and where profit leaks on real jobs.
- [Electrical Estimating Software Pricing in 2026](https://sparkquote.ai/guides/electrical-estimating-software-pricing): What electrical estimating and takeoff software costs in 2026: published prices for 14 tools, first-year cost per estimator, and which vendors only quote.
- [How to Become an Electrical Estimator](https://sparkquote.ai/guides/electrical-estimator-career): What an electrical estimator does, what estimators earn (BLS 2025 data), the skills and software that matter, and a path from the field or from school.
- [Electrician Hourly Rates in 2026: What Customers Pay and What You Should Charge](https://sparkquote.ai/guides/electrician-hourly-rate): What electricians charge per hour in 2026, what they are paid, and how to calculate your own billable rate from wage, burden, overhead and margin.
- [How to Find Electrical Jobs to Bid On](https://sparkquote.ai/guides/find-electrical-jobs-to-bid): Where electrical contractors find jobs to bid: GC bid lists, SAM.gov and state portals, plan rooms, PlanHub and other platforms, plus a bid/no-bid scorecard.
- [Free Electrical Estimating Software: What Is Actually Free](https://sparkquote.ai/guides/free-electrical-estimating-software): Free electrical estimating software in 2026: which tools are free to use, which are free trials, and what each free option limits. Checked against vendor pages.
- [How to Bid Electrical Jobs (Without Leaving Money on the Table)](https://sparkquote.ai/guides/how-to-bid-electrical-jobs): How to bid electrical jobs that win and make money: scope review, takeoff, labor, overhead, margin and exclusions, with residential and commercial examples.
- [How to Estimate Residential Electrical Work](https://sparkquote.ai/guides/how-to-estimate-electrical-work): Estimate residential electrical work by square foot, per device or with labor units: a room-by-room takeoff checklist and a worked whole-house estimate.
- [NECA Labor Units Explained](https://sparkquote.ai/guides/neca-labor-units): What the NECA Manual of Labor Units is, how its Normal, Difficult and Very Difficult columns work, how to adjust units, and how to build your own.

## Templates

- [Free Electrical Templates](https://sparkquote.ai/templates): Free templates for electrical contractors: an estimate template with labor units and margin, a bid proposal template, and an invoice template for progress billing.
- [Electrical Bid Proposal Template](https://sparkquote.ai/templates/electrical-bid-proposal-template): Free electrical bid proposal template with scope, inclusions, exclusions, alternates, unit prices and terms, plus sample language for commercial bids.
- [Free Electrical Estimate Template](https://sparkquote.ai/templates/electrical-estimate-template): Free electrical estimate template with material, labor-unit, overhead and margin sections built in, plus a filled-in 200 amp service upgrade example.
- [Free Electrical Invoice Template](https://sparkquote.ai/templates/electrical-invoice-template): Free electrical invoice template for service calls and progress billing, with labor, material, retainage and change-order lines, plus worked examples.

## Estimating software comparisons

- [Electrical Estimating Software Compared](https://sparkquote.ai/compare): Accubid, ConEst, Countfire, McCormick, PlanSwift, STACK, TurboBid and Procore Estimating compared for electrical contractors: platform, pricing and best fit.
- [7 Best Accubid Alternatives for Electrical Contractors in 2026](https://sparkquote.ai/compare/accubid-alternative): The 7 best Trimble Accubid alternatives for 2026: SparkQuote, Estimation MEP, ConEst, McCormick, STACK, PlanSwift and TurboBid, with prices and best fit.
- [ConEst IntelliBid Alternative](https://sparkquote.ai/compare/conest-alternative): ConEst IntelliBid and SureCount vs. SparkQuote: databases, labor factoring, supplier pricing, takeoff, platform and price, and when IntelliBid fits better.
- [Countfire Alternative for Electrical Contractors](https://sparkquote.ai/compare/countfire-alternative): Countfire vs. SparkQuote for electrical estimating: 2026 pricing, AI symbol counting, labor units, proposals, and when Countfire is still the better choice.
- [Esticom Alternative for Electrical Contractors](https://sparkquote.ai/compare/esticom-alternative): What happened to Esticom, how Procore Estimating works and is priced today, and how it compares with SparkQuote for electrical contractors not on Procore.
- [McCormick Estimating Alternative](https://sparkquote.ai/compare/mccormick-estimating-alternative): McCormick Systems vs. SparkQuote for electrical estimating: NECA labor units, database, takeoff, platform and cost, and when McCormick is the better choice.
- [7 Best PlanSwift Alternatives for Electrical Contractors in 2026](https://sparkquote.ai/compare/planswift-alternative): The 7 best PlanSwift alternatives for 2026: SparkQuote, STACK, Togal.AI, BuildVision, Countfire, TurboBid and Trimble Estimation MEP, with prices and best fit.
- [STACK Estimating Alternative for Electrical Contractors](https://sparkquote.ai/compare/stack-estimating-alternative): STACK Takeoff & Estimate vs. SparkQuote for electrical contractors: 2026 pricing, free plan limits, AI takeoff, labor units, and when STACK fits better.
- [TurboBid Alternative for Electrical Contractors](https://sparkquote.ai/compare/turbobid-alternative): TurboBid vs. SparkQuote for electrical estimating: 2026 pricing, Windows vs. browser, takeoff, price updates, labor units, and when TurboBid is the better choice.

## Product (free beta)

- [AI Electrical Estimating: What It Does, What It Doesn't, and How to Test It](https://sparkquote.ai/ai-electrical-estimating): How AI electrical estimating software works: legend-based symbol detection, human review, labor units and pricing. Where it fails, and how to test it.
- [Electrical Bidding Software](https://sparkquote.ai/electrical-bidding-software): Electrical bidding software that turns PDF plans into a priced bid and proposal, tracks every bid you send, and shows your win rate by customer and job type.
- [Electrical Estimating Services: Outsource It, or Do It Faster In-House?](https://sparkquote.ai/electrical-estimating-services): Outsourced electrical estimating services vs. in-house estimating with AI: cost per bid, turnaround, control of labor units, and a break-even example.
- [Electrical Estimating Software That Does the Takeoff for You](https://sparkquote.ai/electrical-estimating-software): Electrical estimating software for contractors: AI counts devices on your PDF plans, your labor units and prices apply, and the proposal is ready to send.
- [Your AI Electrical Estimator](https://sparkquote.ai/electrical-estimator): An AI electrical estimator that counts your plans, applies your labor units and prices, and drafts the bid, so your people focus on scope and judgment.
- [Electrical Takeoff Software](https://sparkquote.ai/electrical-takeoff-software): Electrical takeoff software for electrical contractors: AI counts devices from the plan legend, measures runs, and works out conduit and wire lengths. Free beta.
- [Electrician Software Built Around Estimating](https://sparkquote.ai/electrician-software): Electrician software built around the job that decides profit: estimating. AI takeoff, labor units and proposals, next to your field-service tools.
- [Low Voltage Estimating Software](https://sparkquote.ai/low-voltage-estimating-software): Low voltage estimating software for data, security, fire alarm and AV contractors: AI counts devices on PDF plans, then builds cable by run and labor by device.
- [Pricing](https://sparkquote.ai/pricing): SparkQuote is free during the beta: AI counts devices on your PDF plans and builds the estimate and proposal. Planned plans and other tools' prices.

## About

- [How We Build and Check Our Calculators](https://sparkquote.ai/about/how-we-build-our-calculators): The sources, code editions, test cases and review process behind our free electrical calculators and reference charts, and what the tools don't account for.
- [Privacy Policy](https://sparkquote.ai/privacy): What SparkQuote collects when you use the site and the free calculators: analytics, session recordings, cookies, who processes the data, and how to opt out.
- [Security and AI Data Use](https://sparkquote.ai/security): How SparkQuote protects your plans and estimates: who sees them, where they are stored, what the AI sees, how links and tokens work, and how to leave.
- [Terms of Use](https://sparkquote.ai/terms): Terms for sparkquote.ai: the SparkQuote app (free beta), free electrical calculators, templates and MCP server, what they are for, and our limits of liability.