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E6B Calc

How to calculate an aircraft's center of gravity: weight and balance step by step

Multiply each weight by its arm to get a moment, add up the weights, add up the moments, divide total moment by total weight. That's the center of gravity. Setting up an aircraft's profile takes maybe ten minutes with the weighing report open next to the phone; checking a load after that takes under a minute. E6B Calc's Weight & Balance does the arithmetic and the envelope check, free for one aircraft.

3 min read · Updated 2026-09-11

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Why the CG matters

Too heavy and it climbs poorly and stresses the structure. Too far forward and it may not want to rotate or flare right. Too far aft and recovering from a stall gets genuinely harder, not just uncomfortable. The CG envelope in the POH is the one safe box for weight and CG together — outside it, none of the performance numbers in the rest of the POH are guaranteed to mean anything.

The three numbers you need for every item

  • Weight: people, bags, fuel and the aircraft's empty weight.
  • Arm: the distance from the datum given in the POH, usually in inches (or cm).
  • Moment: weight × arm. Total moment ÷ total weight = CG.

Fuel gets weighed, not measured in gallons. Planning density is 6.0 lb per US gallon for avgas and mogas, 6.7 for Jet A — 40 US gallons of avgas is 240 lb, not 40 of anything on the moment side of the sheet.

Set up your aircraft once

  1. On E6B, open Weight & Balance and tap Add aircraft.
  2. Give it a Name and a Registration, pick lb and inches or Kilograms and centimetres, and choose the Fuel type: Avgas 100LL, Jet A or Mogas.
  3. Type the Empty weight, Empty arm and Max gross weight from your aircraft's weighing report and POH. For %MAC, add the Leading edge of MAC and MAC length.
  4. Under Stations, tap Add station for each seat row, baggage area and tank, with its Arm, a Usual load and any Placard limit. Switch on This is a fuel tank for tanks.
  5. Under CG envelope, tap Add vertex for each corner of the POH chart (weight and CG), at least three.

Load it for today's flight

  1. Tap the aircraft to open its load sheet.
  2. Type each station's weight, and fuel in gallons or litres: the app turns it into weight by fuel type.
  3. Read Total weight, Centre of gravity and, if set, Percent MAC, plus the verdict and the point plotted on the envelope chart.
  4. Tap Save to history to keep the load.

Worked example

The aircraft below is made up for the example, not a real type. Use your own POH numbers, obviously.

Example load sheet in lb and inches
ItemWeight (lb)Arm (in)Moment (lb-in)
Empty aircraft1,50039.058,500
Front seats34037.012,580
Rear seats15073.010,950
Fuel, 40 gal Avgas 100LL24048.011,520
Baggage5095.04,750
Total2,28043.11 (CG)98,300

98,300 ÷ 2,280 = 43.11 in. The example envelope runs (1,500 lb, 35.0) → (1,950 lb, 35.0) → (2,400 lb, 38.5) → (2,400 lb, 47.3) → (1,500 lb, 47.3), so at 2,280 lb the forward limit sits near 37.6 in and the app reads Within limits. Top off to 50 gallons and add 120 lb of baggage, though, and the total jumps to 2,410 lb at 44.74 in — over gross by 10 lb, which is the kind of thing that's easy to miss doing the arithmetic by hand and obvious the second the app flags it.

Common mistakes

  • Using a sister aircraft's empty weight. Every airframe is weighed on its own; use yours.
  • Checking takeoff only. Fuel burns off, so check the landing CG too, especially with aft baggage.
  • Leaving out the envelope: without one the app shows No envelope on file — CG not checked.
  • Ignoring placard limits. A baggage area has its own maximum even when the total is fine.

The free version keeps one aircraft; E6B Pro adds unlimited profiles. There is no aircraft library and no export or printing of the load sheet.

Questions and answers

Does the app have my aircraft's data?
No. It deliberately ships no aircraft library: you copy your own empty weight, arms and envelope from the weighing report and POH.
Can I work in kilograms?
Yes. Choose Kilograms and centimetres when you create the aircraft; tanks are then in litres. Each aircraft keeps its own units.
What is percent MAC?
The CG expressed as a percentage of the mean aerodynamic chord, used mostly for larger aircraft. Add the leading edge of MAC and its length to the profile to see it.
Is weight and balance free?
Yes, for one aircraft with the full load sheet, envelope chart and limits check. More aircraft need E6B Pro.

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