# General Mass Calculations: Fuel Density, Standard Masses, and LMC

> Understand practical mass calculations for dispatch, including fuel volume-to-mass conversion, passenger standard masses, and last-minute change handling.

- **Subject:** 031 — Mass and Balance
- **Section:** 031-02 — Loading
- **Topic code:** 031-02-03
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/mass-and-balance/loading/mass-calculations/

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## Calculating Total Mass

The total mass of the aircraft is the sum of all its components:
1.  Start with **Basic Empty Mass (BEM)**.
2.  Add **Crew** and **Pantry** to get **Dry Operating Mass (DOM)**.
3.  Add **Traffic Load** (Passengers + Bags + Cargo) to get **Zero Fuel Mass (ZFM)**.
4.  Add **Take-off Fuel** to get **Take-Off Mass (TOM)**.

## Fuel Calculations

Fuel is often measured in volume (Litres or US Gallons) but must be converted to mass (kg or lbs) for weight and balance calculations.

*   **Formula**: $\text{Mass} = \text{Volume} \times \text{Density (SG)}$
*   **Specific Gravity (SG)**: The ratio of the density of the fuel to the density of water.
    *   Jet A-1 SG $\approx 0.8$ (ranges 0.78 - 0.84).
    *   Avgas SG $\approx 0.72$.

*Example*: 1000 Litres of Jet A-1 at SG 0.8
$$
\text{Mass} = 1000 \times 0.8 = 800 \text{ kg}
$$

## Passenger Mass

For large aircraft, standard masses are often used for passengers and baggage to simplify calculations, rather than weighing each individual.

*   **Standard Mass**: A statistical average value set by the authority (e.g., EASA) which includes hand baggage.
*   **Actual Mass**: Used when standard masses are not applicable (e.g., small aircraft with fewer than 10 seats, or non-standard flights).

## Adjustments

Always account for:
*   **Last Minute Changes (LMC)**: Additions or removals of passengers/cargo after the load sheet is finalized.
*   Total mass must be recalculated to ensure limits are not exceeded.

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.