What is the datum in weight and balance?

The datum is an arbitrary vertical reference plane from which all arm distances are measured. It is defined differently for each aircraft — it may be the firewall, the nose, a point ahead of the nose, or any other reference fixed in the POH. All arms in this calculator must use the same datum as your aircraft POH.

A moment is the product of a weight and its arm (distance from the datum). Moment = Weight x Arm. The unit is pound-inches (lb-in) or kilogram-centimeters (kg-cm). Summing all moments and dividing by total weight gives the center of gravity arm.

What happens if the CG is forward of limits?

A forward CG makes the aircraft nose-heavy. The elevator must produce more download to maintain level flight, increasing induced drag and potentially limiting up-elevator authority needed for rotation or flare. In extreme cases it can prevent rotation or recovery from low-speed flight.

What happens if the CG is aft of limits?

An aft CG reduces longitudinal stability. The aircraft may pitch up uncommanded and become difficult or impossible to recover from a stall or spin. An aft CG out of limits is generally considered more dangerous than a forward CG out of limits.

How do I find arm values for my aircraft?

Arms for each standard station (pilot, front passenger, rear seats, baggage, fuel) are published in Section 6 (Weight and Balance) of your aircraft Pilot Operating Handbook (POH) or Airplane Flight Manual (AFM). Some aircraft use moment tables instead of arm values — convert by dividing the published moment by the standard weight for that station.

Should I use actual weight or standard weight for people?

FAA regulations require actual weights or, under certain conditions, standard weights (190 lb / 86 kg for adults in general aviation per AC 120-27). For private operations use actual weights. For charter or commercial operations consult the applicable FAA Advisory Circular for your operation.

Weight and Balance Calculator

Name: Weight and Balance Calculator
Availability: InStock
Author: Nham Vu

Enter station arms and weights for up to 12 load items to compute total weight, moment, and CG position, then verify it falls within your aircraft envelope.

Aircraft Setup

Unit System

Fwd CG Limit (in)

Aft CG Limit (in)

CG limits from your aircraft POH/AFM envelope. Leave blank to skip limit check.

Load Stations

Station Name

Arm (in)

Weight (lb)

Fill in station arms and weights, then click Calculate.

CG arm, total weight, and envelope status will appear here.

Total Weight

CG Arm

Total Moment

lb-in

Fwd limit Aft limit

Forward Aft

Station Breakdown

Station	Arm (in)	Weight (lb)	Moment

Summary

Enter station arms and weights for up to 12 load items to compute total weight, moment, and CG position, then verify it falls within your aircraft envelope.

How it works

Select your preferred unit system (pounds/inches or kilograms/centimeters).
Enter the arm (distance from datum) for each load station — use values from your aircraft POH weight and balance data.
Enter the actual weight for each occupied station (pilot, co-pilot, passengers, baggage, fuel).
Click Calculate to compute individual moments, total weight, total moment, and CG arm.
Enter your aircraft forward and aft CG limits from the POH CG envelope chart.
Read the status banner to see whether the CG is within limits, forward, or aft of the envelope.

Use cases

Pre-flight weight and balance check for general aviation aircraft.
Flight school instruction on CG effects and loading theory.
Verify compliance with MTOW and CG limits before passenger flights.
Experiment with fuel load and passenger seating to find a balanced configuration.
Check Part 135 charter weight and balance documentation requirements.
Cross-check aircraft POH weight and balance tables for homebuilts or experimentals.
Train student pilots on moment arm arithmetic and datum reference.
Convert between imperial and metric weight and balance data.

Frequently Asked Questions

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Last updated: 2026-05-29 · Reviewed by Nham Vu