SizingKitCircuit loading
Amperage Calculator
Add everything on the circuit, line by line, and this free calculator carries a running total in amperes against the breaker protecting it — no signup, no account. Loads expected to run three hours or more are taken at 125 percent under NEC 210.20(A), which is the same rule as never loading a device past 80 percent, and the page names the line at which the total goes over.
- 100% free
- No signup
- Unlimited lines
- 125% continuous applied
- Prints as a schedule
Standard ratings only, from NEC 240.6(A). A device rated 63 A is not on that list and is not an answer.
The schedule
Three placeholder lines are loaded so the totals move — overwrite them. Tick continuous for anything expected to run three hours or more, which is how Article 100 defines it.
Connected, added straight
26.7 A
Minimum device rating
28.3 A
| Line | Rating | Amps | Running |
|---|---|---|---|
| Line 1 | 1 × 1200 VA | 10 A | 10 A |
| Line 2continuous | 1 × 800 VA | 6.67 A | 18.3 A |
| Line 3 | 2 × 5 A | 10 A | 28.3 A |
| Continuous, at 1.25× | 6.67 A | 8.33 A | |
| Everything else, at 100% | 20 A | 20 A | |
| Smallest standard device that covers it | 30 A | ||
The schedule needs a device of at least 28.3 A and the one selected is 20 A, so this circuit is over as drawn. It goes over at Line 3, which is highlighted in the table. Continuous load is what pushed it: 6.67 A of the total is taken at 1.25, adding 1.67 A that no meter would ever read. The next standard rating up is 30 A, and the conductors have to be able to carry that rating before it means anything.
This adds connected load at 100% and applies one rule to it. A service or feeder calculation under NEC Article 220 is a different document: it works in volt-amperes per square foot, adds the small-appliance and laundry branch circuits as fixed figures, and then applies demand factors in steps that let a dwelling with 60 kVA connected take a 200 A service. None of those figures are reproduced on this site, so a whole-house number must come from Article 220 itself rather than from a total added here.
NEC (NFPA 70) 2023, 210.20(A) for branch circuits, 215.3 for feeders and 230.90(A) for services: where a branch circuit supplies continuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load. 'Continuous load' is defined in Article 100 as a load where the maximum current is expected to continue for 3 hours or more.
How to total a circuit and see where it runs out
A schedule, not a conversion — the answer only means anything once everything on the circuit is in the list.
Set the circuit up first
Give the voltage the loads sit across, say whether it is single- or three-phase, and pick the device protecting it from the standard ratings of NEC 240.6(A). Only ratings on that list appear, because a calculated 63 A is not a breaker you can buy and rounding to one is the error the list exists to prevent.
Enter each load in whatever unit its label uses
Volt-amperes is the unit a load calculation is properly written in, nameplate amperes is the most reliable figure when a plate gives it, and watts is accepted but treated as volt-amperes at unity power factor, which is low for anything with a motor or a rectifier in it. Set the quantity where several identical items sit on the same circuit.
Tick what runs three hours or more, then read the running column
Article 100 defines a continuous load by duration, not by what the equipment is, so a sign transformer and a bank of chargers count while a toaster does not. The running column shows the minimum device rating as each line is added, so the line that takes the circuit past the breaker is visible rather than inferred from a final total.
Rules applied, and their limits
| Continuous-load multiplier | 1.25, from NEC 210.20(A) for branch circuits, 215.3 for feeders and 230.90(A) for services. Article 100 defines continuous as three hours or more. |
|---|---|
| The same rule from the other end | 1 ÷ 1.25 = 0.80, so a 20 A device holds 16 A of continuous load and a 100 A device holds 80 A. Both statements are the same requirement. |
| Device ratings offered | Every standard breaker rating of NEC 240.6(A) up to 600 A — 15, 20, 25, 30, 35, 40, 45, 50, 60, 70 and so on. Non-standard ratings are not offered at all. |
| Units a line accepts | Volt-amperes, watts or amperes, with quantity per line. A watt is added as a volt-ampere and the summary says so, since that is exact for resistance and low for everything else. |
| Three-phase handling | Volt-amperes are divided by 1.732 times the line-to-line voltage, so a 3,600 VA three-phase load at 208 V contributes 9.99 A per line rather than 17.3 A. |
| Demand factors applied | None. Every line is added at 100 percent of what you entered before the continuous multiplier, which is correct for a branch circuit and wrong for a dwelling service. |
| Article 220 figures reproduced | None — not the 3 VA per square foot, not the small-appliance and laundry branch allowances, not the stepped demand factors. Those come from the code book. |
| What it prints | The schedule, the two subtotals and the smallest standard device that covers them, sized for a sheet of paper with the input controls dropped. |
| Where it runs | In this tab. A schedule you type is never uploaded and is gone when you close the page. |
Frequently asked questions
What actually counts as a continuous load?
Any load whose maximum current is expected to continue for three hours or more — the definition in Article 100 is about duration and nothing else. Store lighting, a sign circuit, an EV charger and a bank of servers qualify; a kettle, a hand dryer and a table saw do not, however hard they work while running. The equipment type is irrelevant, which is why the tick box on each line asks about hours rather than about what the thing is.
Is the 125 percent rule the same thing as the 80 percent rule?
Yes — they are one requirement written from opposite ends, and 1 ÷ 1.25 = 0.80 exactly. NEC 210.20(A) says the device rating must be at least the noncontinuous load plus 125 percent of the continuous load; the trade says never load a breaker past 80 percent. Trouble only starts when somebody applies both in sequence, multiplying a load by 1.25 and then also derating the breaker to 80 percent, which double-counts and buys a device two sizes too large.
Can I use this to size a house service?
No, and the difference is large enough to matter: this page adds connected load at 100 percent, while a dwelling calculation under Article 220 applies demand factors in steps. A house with 60 kVA of connected equipment routinely lands on a 200 A service precisely because those factors assume the range, the dryer and the air conditioning are not all at maximum at once. Use this for a branch circuit or a panel schedule you want totalled honestly, and the code book's Article 220 for anything a utility or an inspector will look at.
Why does adding a load in watts give a smaller current than the same figure in VA?
It does not — this page treats them as equal, and that is the assumption to be aware of. Watts and volt-amperes are only the same number at unity power factor, so entering a motor's 1,500 W where its 1,875 VA belongs understates the line by a fifth. Convert the watt figure first if the load is anything other than a resistance, then enter the volt-amperes here.
Does the answer mean the conductors are big enough?
No — the device rating and the conductor ampacity are two separate requirements and this page only computes the first. A 50 A breaker is meaningless on conductors good for 40 A, and ampacity itself moves with insulation rating, ambient temperature, how many current-carrying conductors share the raceway and what the terminations are listed for. Nothing on this page is a verdict on an installation; the arithmetic is one input to a decision an engineer or the inspector of record signs off.
How do I enter a three-phase load on the schedule?
Set the circuit to three-phase and enter each load's total volt-amperes, not its per-phase share. The page divides by 1.732 as well as by the line-to-line voltage, so a balanced 3,600 VA load at 208 V shows as 9.99 A per line. An unbalanced single-phase load fed from one leg of a three-phase panel does not belong on the same schedule at all, because its current appears on two conductors and not three.
What happens to the total when I remove a line?
Everything recomputes, including which line the circuit goes over at — the highlight moves rather than staying where it first appeared. The running column is cumulative in the order the lines are listed, so reordering the schedule changes where the crossing shows up without changing the final total. That is worth knowing when you are deciding which load to move to another circuit.
About continuous load, the 80 percent rule and what a schedule cannot tell you
The reason a circuit total is not simply a sum is heat, and the heat is in the device rather than in the load. A molded-case breaker is calibrated to carry its rating indefinitely in open air at a stated ambient, and inside a loaded panelboard next to other breakers it runs warmer than that; the 125 percent in NEC 210.20(A) buys back the margin. The rule is written on the load side, but everything it protects — the terminations, the busbar, the conductor insulation — is on the equipment side, which is why the multiplier applies to the device rating and not to the conductor separately.
A schedule is also the point at which the individual conversions stop being interesting. Getting one appliance from watts to amperes is a division, and the watts to amps calculator does exactly that for a single nameplate; what decides whether the circuit works is the seventh item, the one somebody adds two years later. That is the argument for keeping the list rather than the answer. If the total you build here is heading for a transformer or a standby set rather than a breaker, the kVA to amps calculator takes it from the other side, and the generator size calculator adds the motor starting surge that a running total by definition does not contain.
Two limits are worth stating plainly. This adds connected load, so it is honest for a branch circuit and deliberately pessimistic for a service, where Article 220’s demand factors exist precisely because a building never runs everything at once — those figures are not reproduced on this site and have to come from the code book. And a device rating that the schedule fits inside says nothing about the conductors, the terminations or the ambient the panel lives in. What the page gives you is arithmetic against one article, printed with the article named, so that the person who signs the work is checking a stated calculation rather than a black box.
Where the schedule you type lives
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.
The schedule is held in the page’s own memory and nothing else — there is no account to save it to and no draft kept between visits, so print or copy it before closing the tab if you want to keep it.