The calculator
Runs in your browser. Inches or millimetres at the top. Length and width for a rectangle, or the area for any other shape. Everything after the size is optional and only needed for weight and balance.
How the formula works
Weight = area × thickness × density. With area in square inches, thickness in inches and density in pounds per cubic inch, the answer is in pounds. Per square foot, that is thickness × 144 × density: 0.032" 2024 is 0.032 × 144 × 0.100 = 0.461 lb/ft².
The densities. MIL-HDBK-5J gives one density per alloy in its design property tables: 0.100 lb/in³ for 2024, 0.101 for 2014, 2017 and 7075, 0.098 for 6061, 0.097 for 5052, and 0.283 for 4130 steel. The handbook gives the same figure for the bare and clad versions of 2014, 2024 and 7075. Temper does not change it either: the figure sits in the table for the alloy, across every temper listed.
Moment = weight × arm. AC 43.13-1B par. 10-2 defines the arm as the horizontal distance in inches from the datum to the item's center of gravity: plus aft of the datum, minus forward. For a flat patch, the c.g. is its geometric center. Weight removed counts too: trimming out damaged skin takes weight and moment away before the doubler adds them back.
When it matters. Par. 10-2c sets what counts as a negligible weight change: 1 lb or less for aircraft under 5,000 lb empty, 2 lb from 5,000 to 50,000 lb, 5 lb above that. A single sheet-metal doubler almost always comes in under the threshold. Several in one repair, or a steel part, may not.
Weight per square foot, by thickness
Pounds per square foot, from the MIL-HDBK-5J densities. 2014, 2017 and 7075 share a column because they share a density.
| Thickness | 2024 (0.100) | 7075, 2014, 2017 (0.101) | 6061 (0.098) | 5052 (0.097) |
|---|---|---|---|---|
| 0.016" | 0.230 | 0.233 | 0.226 | 0.223 |
| 0.020" | 0.288 | 0.291 | 0.282 | 0.279 |
| 0.025" | 0.360 | 0.364 | 0.353 | 0.349 |
| 0.032" | 0.461 | 0.465 | 0.452 | 0.447 |
| 0.040" | 0.576 | 0.582 | 0.564 | 0.559 |
| 0.050" | 0.720 | 0.727 | 0.706 | 0.698 |
| 0.063" | 0.907 | 0.916 | 0.889 | 0.880 |
| 0.071" | 1.022 | 1.033 | 1.002 | 0.992 |
| 0.080" | 1.152 | 1.164 | 1.129 | 1.117 |
| 0.090" | 1.296 | 1.309 | 1.270 | 1.257 |
| 0.100" | 1.440 | 1.454 | 1.411 | 1.397 |
| 0.125" | 1.800 | 1.818 | 1.764 | 1.746 |
Aircraft Spruce's listing for 2024-T3 sheet gives the same figures, rounded: 0.461 lb/ft² for 0.032", 0.576 for 0.040", 0.907 for 0.063".
Worked example
An external doubler, 8" × 5", in 0.040" 2024-T3, over a fuselage skin repair at station +120". The damaged area of 0.032" skin, 3" × 2", is trimmed out first.
- Doubler: 40 in² × 0.040" × 0.100 = 0.160 lb.
- Removed skin: 6 in² × 0.032" × 0.100 = 0.019 lb.
- Net change: 0.160 − 0.019 = +0.141 lb.
- Moment change: 0.141 × 120 = +16.9 lb-in.
- Aircraft under 5,000 lb empty: the negligible threshold is 1 lb.
+0.141 lb and +16.9 lb-in, well within negligible on weight. The figure leaves out rivets, sealant and primer; add them before writing the change off.
Limits — when NOT to use this
A weight estimate for flat stock. The aircraft's own records govern its weight and balance.
- Nominal thickness, nominal density. Real sheet runs to a thickness tolerance. For a figure that goes into the aircraft's records, weigh the part.
- Fasteners, sealant and finish are not included. On a riveted repair they are a real share of the weight.
- Flat pieces only. A formed part weighs the same as its flat pattern; cut-outs and lightening holes have to come off the area.
- Negligible weight is one of two tests. AC 43.13-1B par. 10-2c also defines a negligible c.g. change: less than 0.05% MAC for fixed wing, 0.2% of the c.g. range for rotorcraft. That needs the aircraft's data.
- Not for composites, magnesium or titanium. They are not in the material list; their densities differ.
Questions people actually ask
How much does a 4 × 8 sheet of 0.032 aluminum weigh?
In 2024: 32 ft² × 0.461 lb/ft² = 14.7 lb. In 6061: 32 × 0.452 = 14.5 lb.
Does clad 2024 weigh more or less than bare?
MIL-HDBK-5J gives both the same density, 0.100 lb/in³. The cladding is a thin layer of nearly pure aluminum; the handbook does not split the difference out.
Do I have to update weight and balance after a patch?
If the change is not negligible. AC 43.13-1B par. 10-2c sets the line at 1 lb for aircraft under 5,000 lb empty, 2 lb up to 50,000 lb, and 5 lb above. It also sets a c.g. threshold. A single doubler is usually under both, but the aircraft's records and your inspector decide.
Is 7075 heavier than 2024?
Slightly: 0.101 against 0.100 lb/in³, so 1% heavier for the same sheet. 6061 is about 2% lighter than 2024.
Sources
- MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003) — density ω in each alloy's design property table: 2024 Tables 3.2.3.0(b1) and (e1) for clad, 0.100; 2014 Tables 3.2.1.0(b1) and (c1), 0.101; 2017 Table 3.2.2.0(b), 0.101; 5052 Table 3.5.1.0(b1), 0.097; 6061 Table 3.6.2.0(b1), 0.098; 7075 Tables 3.7.6.0(b1) and (c1), 0.101; AISI 4130 Table 2.3.1.0(c1), 0.283 lb/in³. Cancelled and replaced by MMPDS; the densities are the handbook's.
- FAA AC 43.13-1B CHG 1, Chapter 10, par. 10-2 — definitions of datum, arm and moment, and par. 10-2c, negligible weight change and negligible c.g. change.
- Aircraft Spruce, 2024-T3 aluminum sheet listing — listed weight per square foot by thickness, used here as a cross-check only.