Weight and Balance CG Margin Calculator — Rex's Toolbox

Rex says

Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.

Try a scenario

Click to load — tweak from there.

Inputs

Empty weight(lb)

Empty weight arm(in)

Front seats total weight(lb)

Front seats arm(in)

Fuel weight(gal)

Fuel arm(in)

Baggage weight(lb)

Baggage arm(in)

Result

Computed CG

41.04

Total weight

2,220

Margin to forward limit (in)

6.04

Margin to aft limit (in)

6.26

Lb over max gross (negative = under)

-230

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How to use this

1Enter empty weight (lb).
2Enter empty weight arm (in).
3Enter front seats total weight (lb).
4Enter front seats arm (in).
5Enter fuel weight (gal).
6Enter fuel arm (in).
7Enter baggage weight (lb).
8Enter baggage arm (in).
9Read your computed cg on the right — it updates as you type.
10Hit Share to keep the scenario or send it to someone.

About this calculator

A basic weight and balance check tells you pass or fail. This one goes further and tells you how many inches of margin you have to each limit, which matters because a CG near the aft limit degrades stall recovery and stability margins even when it's technically within limits. It sums moments from empty weight, pilot/passengers, fuel, and baggage stations, divides by total weight to find CG, and reports the margin to both the forward and aft limits along with whether you're within the max gross weight.

FormulaCG = total moment ÷ total weight, where moment = weight × arm for each station. Margin = CG − forward limit, and aft limit − CG.

Worked example

Using the values the calculator loads with:

Inputs

Empty weight: 1600 lb
Empty weight arm: 39.5 in
Front seats total weight: 340 lb
Front seats arm: 37 in
Fuel weight: 40 gal
Fuel arm: 48 in
Baggage weight: 40 lb
Baggage arm: 95 in

Results

Computed CG: 41.04
Total weight: 2,220
Margin to forward limit (in): 6.04
Margin to aft limit (in): 6.26
Lb over max gross (negative = under): -230

What each field means

Inputs

Empty weight (lb): The empty weight used in the calculation, measured in lb. Starts at 1600 lb so you have a working example on load.
Empty weight arm (in): The empty weight arm used in the calculation, measured in in. Starts at 39.5 in so you have a working example on load.
Front seats total weight (lb): The front seats total weight used in the calculation, measured in lb. Starts at 340 lb so you have a working example on load.
Front seats arm (in): The front seats arm used in the calculation, measured in in. Starts at 37 in so you have a working example on load.
Fuel weight (gal): The fuel weight used in the calculation, measured in gal. Starts at 40 gal so you have a working example on load.
Fuel arm (in): The fuel arm used in the calculation, measured in in. Starts at 48 in so you have a working example on load.
Baggage weight (lb): The baggage weight used in the calculation, measured in lb. Starts at 40 lb so you have a working example on load.
Baggage arm (in): The baggage arm used in the calculation, measured in in. Starts at 95 in so you have a working example on load.

Results

Computed CG: Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Total weight: Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Margin to forward limit (in): Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Margin to aft limit (in): Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Lb over max gross (negative = under): Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

Why use a generic forward/aft limit instead of my POH numbers?

The default limits shown (35.0 to 47.3 inches) are illustrative placeholder values modeled on a common trainer. Every make and model has its own envelope, and some airplanes have limits that shift with total weight rather than being fixed numbers, so you must substitute your specific POH's forward and aft CG limits for a real preflight check.

Why does aft CG matter even if I'm within limits?

As CG moves aft, static longitudinal stability decreases and stall recovery becomes more difficult because there's less elevator authority to counter a nose-up pitching moment. An airplane loaded near the aft limit can still be legal but noticeably less forgiving in slow flight and stalls than one loaded mid-envelope.

How is fuel weight calculated here?

This tool assumes 6 lb/gal for standard 100LL avgas. Jet A weighs about 6.7-6.8 lb/gal depending on temperature, so turbine aircraft or diesel-cycle piston engines need that substituted before trusting the total weight figure.

What if I'm over gross but within CG limits?

Being within the CG envelope doesn't override a max gross weight violation — both must be satisfied independently. Exceeding max gross weight, even by a small margin, is a certification violation with real structural and performance consequences: longer takeoff roll, reduced climb rate, and higher stall speed.

Accuracy and limitations

Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Results are rounded for readability; add a buffer before ordering, booking, or committing.
Double-check anything with a real cost attached against a local quote.

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Cite this calculator

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APA

RevenueLab. (2026). Weight and Balance CG Margin Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/weight-balance-cg-margin

HTML

<p>Source: <a href="https://www.revenuelab.fyi/toolbox/weight-balance-cg-margin" target="_blank" rel="noopener">Weight and Balance CG Margin Calculator — RevenueLab</a> (2026).</p>

Markdown

Source: [Weight and Balance CG Margin Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/weight-balance-cg-margin) (2026).