CG as % MAC Calculator
Convert CG between inches-aft-of-datum and percent of mean aerodynamic chord — the dialect transport aircraft, jets and aerodynamicists speak.
%MAC normalizes CG to the wing instead of an arbitrary datum: 25% MAC means a quarter-chord CG regardless of aircraft size — which is why stability discussions, jet load sheets and stab-trim settings all speak it.
Formula
⚠️ For planning and education only. Weight & balance must be computed from YOUR aircraft's actual empty weight, arm and current equipment list, and verified against the POH/AFM envelope before flight.
Convert CG between inches-aft-of-datum and percent of mean aerodynamic chord — the dialect transport aircraft, jets and aerodynamicists speak.
About CG as % MAC Calculator
Light-aircraft pilots measure CG in inches from a datum the manufacturer chose arbitrarily; transport aviation measures it as a percentage of the mean aerodynamic chord, because aerodynamics happens relative to the wing. This converter translates between the dialects — give it CG, LEMAC and MAC length, get %MAC and the raw distance aft of the leading edge — the exact arithmetic on every airline load sheet and behind every takeoff stab-trim setting.
How to use CG as % MAC Calculator
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula %MAC = (CG − LEMAC) / MAC × 100 substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use CG as % MAC Calculator?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula %MAC = (CG − LEMAC) / MAC × 100 with sources cited on the page
- ✓%MAC normalizes CG to the wing instead of an arbitrary datum: 25% MAC means a quarter-chord CG regardless of aircraft size — which is why stability discussions, jet load sheets and stab-trim settings all speak it.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
What is the mean aerodynamic chord, conceptually?+
The chord of the rectangular wing that would behave, in pitching-moment terms, like your actual tapered/swept wing — a single representative chord with a defined leading-edge position (LEMAC). Expressing CG as a fraction of it locates the CG relative to the wing's aerodynamic center (near 25% MAC), which is what stability actually cares about.
Why do jets set stabilizer trim from %MAC?+
The pitching moment the stab must trim depends on the CG's distance from the wing's aerodynamic center — i.e., on %MAC directly. Load sheets therefore output %MAC, and the crew dials the corresponding trim units before takeoff. A mis-set trim from a wrong %MAC is a classic rotation-anomaly incident chain.
Where do I find LEMAC and MAC for my aircraft?+
In the type's weight & balance manual or POH Section 6 (transport types: the weight and balance control manual). They're fixed geometric constants per type — e.g., a 737-800's MAC is 155.8 in with LEMAC at 625.6 in aft of datum. This tool's defaults sketch that geometry for practice.
Does %MAC matter for my Cessna?+
Functionally no — light-aircraft envelopes are published in inches, and converting adds no operational value. It matters when you step up: turbine transitions, dispatcher exams and load-control roles all assume %MAC fluency. Practicing the conversion on familiar small-plane numbers (it works on any geometry) is cheap preparation.
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