Cessna 172 Weight and Balance Calculator
Safely operate your Cessna 172 by ensuring proper weight and balance compliance.
Cessna 172 Weight & Balance Input
Enter the aircraft's empty weight as listed in the POH.
Center of Gravity for the empty weight (often Station 80.5 for older 172s).
Total weight of pilot and front passenger.
Arm (horizontal distance from datum) for the forward seats.
Total weight of rear seat passengers.
Arm (horizontal distance from datum) for the aft seats.
Weight in the main baggage area. Check POH for limits.
Arm for the main baggage compartment.
Weight in the optional baggage area (if applicable).
Arm for the optional baggage compartment.
6.0 lbs/gallon (Avg. 100LL)
6.7 lbs/gallon (Avg. Jet A)
8.0 lbs/gallon (Avg. Avg. Water)
Select the approximate weight of your fuel.
Total usable fuel onboard.
Arm for the fuel tanks (check POH, often wing root).
Weight & Balance Results
CG: —
Total Weight: — lbs
Total Moment: — in-lbs
CG Location (MAC %): — %
Moment = Weight × Arm
Total Moment = Sum of all individual moments
Total Weight = Sum of all individual weights
CG = Total Moment / Total Weight
CG (MAC %) = ((CG – Datum for MAC) / MAC Length) * 100
(Datum for MAC and MAC Length are specific to the aircraft model and found in the POH.)
Total Moment = Sum of all individual moments
Total Weight = Sum of all individual weights
CG = Total Moment / Total Weight
CG (MAC %) = ((CG – Datum for MAC) / MAC Length) * 100
(Datum for MAC and MAC Length are specific to the aircraft model and found in the POH.)
| Item | Weight (lbs) | Arm (in) | Moment (in-lbs) |
|---|---|---|---|
| Enter data and click Calculate. | |||
Weight & Balance Envelope
Visual representation of your aircraft's current CG relative to the operational limits.
What is Cessna 172 Weight and Balance?
Understanding and accurately calculating the Cessna 172 weight and balance is a fundamental aspect of safe aviation. It ensures that the aircraft operates within its designed performance parameters and within the limits specified by the manufacturer. Weight and balance calculations determine the aircraft's center of gravity (CG), which is the point where the aircraft would balance if suspended. This CG must remain within a specific range, known as the CG envelope, for safe flight. Exceeding the maximum allowable weight or having the CG outside the envelope can lead to loss of control, reduced maneuverability, and potentially a stall or spin. The Cessna 172, a widely used trainer and personal aircraft, has specific weight and balance limitations detailed in its Pilot's Operating Handbook (POH).
Pilots, aircraft owners, and maintenance personnel should use the Cessna 172 weight and balance calculator. This tool is crucial for pre-flight planning, especially when carrying passengers, luggage, or different fuel loads. It helps pilots make informed decisions about how to load the aircraft to maintain safe operation.
A common misconception is that as long as the total weight is below the maximum takeoff weight, the aircraft is automatically safe. However, the location of that weight (the CG) is equally, if not more, critical. An aircraft can be below its maximum weight but still be outside the CG limits, making it unsafe. Another misconception is that weight and balance is a static calculation; in reality, it changes throughout the flight as fuel is consumed and, if applicable, jettisoned.
Cessna 172 Weight and Balance Formula and Mathematical Explanation
The core principle behind weight and balance calculations is the concept of moments. A moment is the product of a weight and its horizontal distance from a reference datum. In aviation, this datum is an arbitrary reference point established by the manufacturer, typically forward of the aircraft's nose. All arms (distances) are measured from this datum.
The primary formula is:
Moment = Weight × Arm
To determine the aircraft's overall weight and balance, we sum the weights and moments of all components:
Total Weight = Sum of all individual weights (Empty Weight + Occupants + Baggage + Fuel, etc.)
Total Moment = Sum of all individual moments (Moment of Empty Weight + Moment of Occupants + Moment of Baggage + Moment of Fuel, etc.)
Once the total weight and total moment are calculated, the aircraft's Center of Gravity (CG) location is found by dividing the total moment by the total weight:
CG (Datum) = Total Moment / Total Weight
This CG value is typically expressed in inches from the datum. However, for regulatory and operational purposes, it's often converted into a percentage of the Mean Aerodynamic Chord (MAC). The MAC is the average chord length of the wing. The formula for CG in MAC percentage is:
CG (MAC %) = ((CG (Datum) – Datum for MAC) / MAC Length) × 100
Where:
- Datum for MAC is the reference point from which the MAC percentage is measured (e.g., the leading edge of the MAC).
- MAC Length is the length of the Mean Aerodynamic Chord.
These specific datum and MAC values are crucial and must be obtained from the aircraft's POH.
Variables Table for Cessna 172 Weight and Balance
| Variable | Meaning | Unit | Typical Range (Cessna 172 specific) |
|---|---|---|---|
| Empty Weight | Weight of the aircraft without pilot, passengers, fuel, or baggage. | lbs | 1200 – 1700 lbs (varies by model and equipment) |
| Empty Weight CG | Center of Gravity location for the empty weight, measured from the datum. | inches from Datum | ~75 – 90 inches (varies) |
| Occupant Weight | Weight of pilot and passengers. | lbs | 0 – 400+ lbs per person |
| Occupant Arm | Horizontal distance of occupant(s) from the datum. | inches from Datum | Forward Seats: ~35-45 in Aft Seats: ~70-80 in |
| Baggage Weight | Weight of items in baggage compartments. | lbs | 0 – 120 lbs (compartment limits vary) |
| Baggage Arm | Horizontal distance of baggage compartment(s) from the datum. | inches from Datum | Baggage 1: ~90-100 in Baggage 2: ~115-130 in |
| Fuel Weight | Weight of fuel onboard. | lbs | Calculated: Gallons × lbs/gallon |
| Fuel Arm | Horizontal distance of fuel tanks from the datum. | inches from Datum | ~35-40 in (wing root) |
| Total Weight | Sum of all weights on board. | lbs | Must be below Max Takeoff Weight (e.g., 2550 lbs for 172N/P) |
| Total Moment | Sum of all moments (Weight x Arm). | in-lbs | Varies significantly |
| CG (Datum) | Calculated CG location relative to the datum. | inches from Datum | Must be within Forward and Aft CG limits. |
| CG (MAC %) | CG location expressed as a percentage of the Mean Aerodynamic Chord. | % | e.g., 15% to 25% MAC (specific to 172 variant) |
| Max Takeoff Weight | The maximum permissible weight for takeoff. | lbs | e.g., 2550 lbs (typical for many 172 variants) |
| Forward CG Limit | The most forward allowable CG position. | inches from Datum or % MAC | e.g., 68.5 inches or ~15% MAC |
| Aft CG Limit | The most aft allowable CG position. | inches from Datum or % MAC | e.g., 96.5 inches or ~25% MAC |
Practical Examples (Real-World Use Cases)
Example 1: Solo Cross-Country Flight
Scenario: A pilot plans a cross-country flight in a Cessna 172 (Max Takeoff Weight: 2550 lbs). The aircraft's empty weight is 1550 lbs with an Empty Weight CG of 82 inches from the datum. The pilot (180 lbs) will occupy the forward seats (arm 38 inches). They plan to carry 30 lbs of baggage in compartment 1 (arm 95 inches) and take off with 40 gallons of usable fuel (using 6 lbs/gallon) from tanks with an arm of 36 inches. The POH specifies forward CG limit at 68.5 inches and aft limit at 96.5 inches.
Inputs:
- Empty Weight: 1550 lbs
- Empty Weight CG: 82 inches
- Forward Seat Weight: 180 lbs
- Forward Seat Arm: 38 inches
- Aft Seat Weight: 0 lbs
- Aft Seat Arm: 73 inches
- Baggage 1 Weight: 30 lbs
- Baggage 1 Arm: 95 inches
- Baggage 2 Weight: 0 lbs
- Baggage 2 Arm: 125 inches
- Fuel Weight/Gal: 6 lbs/gallon
- Fuel Gallons: 40 gallons
- Fuel Arm: 36 inches
Calculations:
- Fuel Weight = 40 gal * 6 lbs/gal = 240 lbs
- Empty Weight Moment = 1550 lbs * 82 in = 127,100 in-lbs
- Forward Seat Moment = 180 lbs * 38 in = 6,840 in-lbs
- Baggage 1 Moment = 30 lbs * 95 in = 2,850 in-lbs
- Fuel Moment = 240 lbs * 36 in = 8,640 in-lbs
- Total Weight = 1550 + 180 + 30 + 240 = 2000 lbs
- Total Moment = 127,100 + 6,840 + 2,850 + 8,640 = 145,430 in-lbs
- CG (Datum) = 145,430 in-lbs / 2000 lbs = 72.715 inches
Results & Interpretation:
- Total Weight: 2000 lbs (Well below 2550 lbs Max Takeoff Weight)
- CG Location: 72.715 inches from datum
- CG Envelope Check: The calculated CG (72.715 inches) is within the specified limits of 68.5 inches (forward) and 96.5 inches (aft).
This configuration is safe for takeoff. The pilot has plenty of capacity for additional weight or baggage while remaining within limits.
Example 2: Four Adults and Full Fuel
Scenario: The same Cessna 172 (EW: 1550 lbs, EW CG: 82 in). Four adults plan to fly: pilot (170 lbs), front passenger (160 lbs), two rear passengers (140 lbs each). They want to take off with full usable fuel (48 gallons, 6 lbs/gallon). Baggage is limited to 10 lbs in compartment 1.
Inputs:
- Empty Weight: 1550 lbs
- Empty Weight CG: 82 inches
- Forward Seat Weight: 170 + 160 = 330 lbs
- Forward Seat Arm: 38 inches
- Aft Seat Weight: 140 + 140 = 280 lbs
- Aft Seat Arm: 73 inches
- Baggage 1 Weight: 10 lbs
- Baggage 1 Arm: 95 inches
- Fuel Weight/Gal: 6 lbs/gallon
- Fuel Gallons: 48 gallons
- Fuel Arm: 36 inches
Calculations:
- Fuel Weight = 48 gal * 6 lbs/gal = 288 lbs
- Empty Weight Moment = 1550 lbs * 82 in = 127,100 in-lbs
- Forward Seat Moment = 330 lbs * 38 in = 12,540 in-lbs
- Aft Seat Moment = 280 lbs * 73 in = 20,440 in-lbs
- Baggage 1 Moment = 10 lbs * 95 in = 950 in-lbs
- Fuel Moment = 288 lbs * 36 in = 10,368 in-lbs
- Total Weight = 1550 + 330 + 280 + 10 + 288 = 2458 lbs
- Total Moment = 127,100 + 12,540 + 20,440 + 950 + 10,368 = 171,398 in-lbs
- CG (Datum) = 171,398 in-lbs / 2458 lbs = 69.73 inches
Results & Interpretation:
- Total Weight: 2458 lbs (Below 2550 lbs Max Takeoff Weight)
- CG Location: 69.73 inches from datum
- CG Envelope Check: The calculated CG (69.73 inches) is within the specified limits of 68.5 inches (forward) and 96.5 inches (aft). It is very close to the forward limit.
This configuration is also safe, but operating close to the forward CG limit requires careful attention. Any reduction in forward weight (e.g., lighter occupants) or increase in aft weight (e.g., more baggage) could push the CG outside the forward limit. This highlights the importance of precise calculations for every flight.
How to Use This Cessna 172 Weight and Balance Calculator
- Gather Aircraft Data: Locate your Cessna 172's Pilot's Operating Handbook (POH). Find the section detailing the aircraft's Empty Weight, Empty Weight Center of Gravity (EWCG), maximum takeoff weight, and the forward and aft CG limits (often expressed in inches from datum or as a percentage of MAC).
-
Input Basic Weights:
- Enter your aircraft's Empty Weight and its corresponding Empty Weight CG (arm).
- Enter the total weight of the pilot and front passenger(s) in the Forward Seats Occupant(s) Weight field.
- Enter the arm (distance from datum) for the forward seats.
- Repeat for any passengers in the Aft Seats.
-
Input Payload:
- Enter the weight of baggage in Baggage Compartment 1 and its arm. If you have an optional second baggage area, enter its weight and arm.
- Select the appropriate fuel density (lbs/gallon) from the dropdown, typically 6.0 lbs/gallon for 100LL avgas.
- Enter the total quantity of usable Fuel Gallons you plan to take.
- Enter the arm for the fuel tanks (this is usually constant and found in the POH, often near the wing root).
- Calculate: Click the "Calculate" button.
-
Review Results:
- Primary Result: The calculated CG location (in inches from the datum) will be displayed prominently.
- Intermediate Values: You'll see the Total Weight and the Total Moment. The CG will also be shown as a percentage of MAC if the POH provides the necessary datum and MAC length to calculate it (this calculator focuses on the primary CG datum calculation).
- Summary Table: A table breaks down the weight and moment for each item added to the aircraft.
- Chart: The chart visually plots your current CG position against the aircraft's operational envelope (forward and aft limits).
- Interpret and Decide: Compare your calculated CG to the forward and aft CG limits specified in your POH. Ensure the Total Weight is below the Maximum Takeoff Weight. If the CG is within limits and the weight is acceptable, your aircraft is loaded safely. If outside limits, you must redistribute weight (move baggage, reduce fuel, etc.) or adjust passengers/pilot to achieve a safe configuration.
- Reset: Click "Reset" to clear all fields and start over.
- Copy: Click "Copy Results" to copy the key calculated values to your clipboard for documentation or further use.
Key Factors That Affect Cessna 172 Results
Several factors influence the Cessna 172 weight and balance calculations and the final CG position. Understanding these is vital for safe flight planning:
- Empty Weight and CG Variation: The aircraft's Empty Weight and EWCG are not static. They change over time due to modifications, repairs, or equipment additions/removals. It's crucial to maintain an up-to-date Weight and Balance manifest. Even minor equipment changes can shift the EWCG.
- Passenger and Pilot Weights: The weight of individuals is a direct contributor to both total weight and total moment. Variations in passenger weight can significantly impact the CG, especially in smaller aircraft or when flying near CG limits. The average weights used in calculations should reflect the actual load.
- Baggage Loading: The location (arm) and weight of baggage are critical. Heavier baggage loaded further aft will move the CG aft. Conversely, lighter baggage or baggage loaded forward will move the CG forward. Always adhere to baggage compartment weight limits and CG arm constraints.
- Fuel Load: Fuel is often the most significant variable weight component. Since fuel tanks are typically located near the wings' center (affecting the arm), the fuel's weight distribution significantly influences the CG. As fuel burns off during flight, the total weight decreases, and the CG typically moves forward as the fuel moment becomes less dominant relative to the remaining weight.
- Aircraft Model Specifics: Different Cessna 172 models (e.g., 172A, 172M, 172SP, 172R, 172S) have different maximum weights, CG envelopes, and arm values for various stations. Always use the POH specific to your aircraft's model and serial number.
- Equipment and Modifications: Installing avionics, STOL kits, different engines, or interior upgrades alters the aircraft's empty weight and CG. These changes must be properly documented and incorporated into the aircraft's official Weight and Balance record.
- Datum and Arm Reference Points: The accuracy of the calculation hinges on using the correct datum and consistent arm measurements as defined in the POH. An incorrect datum or arm can lead to completely erroneous CG calculations.
- Usable vs. Unusable Fuel: Only usable fuel should be included in the takeoff weight and balance calculation. Unusable fuel is not available for use and is therefore not factored into the moment calculation for takeoff.
Frequently Asked Questions (FAQ)
What is the maximum takeoff weight for a Cessna 172?
This varies by model. For many common variants like the 172N, 172P, and 172R/S, it is 2550 lbs (1157 kg). Older models might have lower limits (e.g., 2300 lbs). Always consult your specific aircraft's POH.
What are the typical CG limits for a Cessna 172?
Limits also vary by model. A common range for the forward CG limit is around 68.5 inches from the datum (approx. 15% MAC), and the aft CG limit is often around 96.5 inches from the datum (approx. 25% MAC). Again, check your POH.
Can I fly with fuel tanks partially full?
Yes, but you must accurately calculate the weight and moment of the fuel quantity you are carrying. Fuel weight changes significantly impact the overall CG. Flying with less than full tanks often moves the CG forward, which can be beneficial if you are near the aft limit, but detrimental if you are near the forward limit.
How often should I update my aircraft's weight and balance?
You must update the weight and balance record whenever a modification is made to the aircraft that affects its empty weight or CG. This includes installing new avionics, changing interior configurations, or significant repairs. Routine inspections do not typically require an update unless an associated change occurs.
What happens if I exceed the maximum takeoff weight?
Exceeding the maximum takeoff weight reduces aircraft performance (longer takeoff roll, reduced climb rate), increases stall speed, and can place excessive stress on the airframe. It is a serious safety violation.
What happens if my CG is outside the envelope?
If the CG is too far forward, the aircraft may be difficult or impossible to rotate for takeoff and could have a tendency to stall easily. If the CG is too far aft, the aircraft becomes unstable, overly sensitive to control inputs, and much more susceptible to stalling, potentially leading to a spin from which recovery may be difficult or impossible.
Can I use average weights for passengers?
Aviation regulations often allow the use of standard average weights (e.g., 170 lbs or 190 lbs for pilots/adult males, 130 lbs for adult females, 90 lbs for children) for weight and balance calculations, provided they are specified in the POH or aircraft records. However, if you know the actual weight of a passenger and it differs significantly, using the actual weight provides a more accurate result. Always use the weights specified or permitted by your aircraft's documentation.
Where do I find the "datum" and "arm" values for my Cessna 172?
The datum (reference point) and the specific arms for various weight stations (seats, baggage compartments, fuel tanks, empty weight) are detailed in the Pilot's Operating Handbook (POH) for your specific Cessna 172 model. This is critical information for accurate calculations.
Does fuel burn-off affect the CG during flight?
Yes, significantly. As fuel is consumed, the total weight decreases, and because fuel is often located relatively far from the datum (especially in wings), its moment diminishes. This typically causes the CG to move forward. Pilots should perform in-flight CG calculations or be aware of how fuel burn will affect the CG relative to the limits, particularly on longer flights.