Electrician: Panel Load Percent

All versions

Before you add a circuit, you need to know how full the panel already is. SUM the connected loads, divide by the panel rating, and the percentage tells you whether there is room to spare.

Quick formula: Sum the circuit loads, then divide by the panel rating:

=SUM(B2:D2)/E2

A 200 A panel carrying 60 + 45 + 40 = 145 A is running at 72.5% — comfortable; over 80% and it is time to talk about a subpanel.

Functions used (tap for the full reference guide):

SUM

The example

Three panels, each with three circuit loads and the panel's amp rating.

	A	B	C	D	E	F
1	Panel	Circ 1 (A)	Circ 2 (A)	Circ 3 (A)	Rating (A)	Load %
2	Main house	60	45	40	200	72.5%
3	Shop subpanel	40	30	18	100	88.0%
4	Garage	25	20	15	100	60.0%

The formula

SUM totals the loads; the division turns it into a percentage:

=SUM(B2:D2)/E2 // total connected amps / panel rating

How it works

The load percent is total draw over capacity:

SUM(B2:D2) adds the connected load on every circuit — widen the range as you add columns.
E2 is the panel's amp rating (100 A, 200 A, and so on).
Dividing and formatting the cell as a percent shows how much of the panel is spoken for.

The NEC continuous-load rule caps many panels at 80%; keep the percentage below that and you keep your margin.

Try it: interactive demo

Interactive

Enter three circuit loads and the panel rating.

Circuit 1 (A)

Circuit 2 (A)

Circuit 3 (A)

Panel rating (A)

Variations

Flag panels over 80%

Wrap the ratio in IF to print a warning automatically.

=IF(SUM(B2:D2)/E2>0.8,"Full","OK")

Spare capacity in amps

Show the headroom left rather than the percentage used.

=E2-SUM(B2:D2)

Pitfalls & errors

Sum the actual connected or calculated load, not the breaker sizes — breakers routinely total well past the panel rating and that is normal.

Format the result cell as a percentage; a raw 0.725 is easy to misread as 72 whole amps.

Practice workbook

📊

Download the free Electrician: Panel Load Percent practice workbook

Edit the yellow circuit and rating cells; the Load % recalculates.

Frequently asked questions

Should I use breaker sizes or actual load?

Use the calculated or measured load, not the sum of breaker ratings. Breakers protect wire; their total normally exceeds the panel rating and does not reflect real draw.

Why 80%?

The NEC treats many loads as continuous and limits them to 80% of the circuit or panel rating. Staying under 80% keeps you code-compliant and leaves room to grow.

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Function references: SUM