Thermal Expansion of Aluminum: Formula and Examples

Aluminum expands about 22 to 24 micrometers per meter for every 1°C rise, depending on the alloy. That change is small in a short bracket but can be significant in a long handrail, extrusion, sheet, machined assembly, or close-fitting joint. To predict it, identify the aluminum grade, find the temperature change, and apply the linear-expansion formula.

What Thermal Expansion of Aluminum Means

Thermal expansion is the increase in a material’s dimensions as its temperature rises. Aluminum atoms vibrate more as they gain heat, increasing the average spacing between them. When the metal cools, it contracts again.

A free aluminum part expands in all directions. A bar becomes longer, a sheet becomes longer and wider, and a hole in a heated aluminum plate becomes slightly larger rather than smaller.

The important distinction is between expansion and warping:

A free aluminum part normally changes size; it warps only when expansion is uneven or restrained.

A uniformly heated, freely supported rectangular aluminum sheet can grow without noticeably changing shape. But if one face is hotter than the other, one end is clamped, or the part contains residual stress from forming or machining, unequal expansion can make it bow, twist, or buckle.

For a straight part, the basic relationship is:

\[ \Delta L = \alpha \times L_0 \times \Delta T \]

Where:

\(\Delta L\) is the change in length.
\(\alpha\) is the coefficient of linear thermal expansion.
\(L_0\) is the original length.
\(\Delta T\) is the temperature change.

Use a coefficient in ppm/°F with a temperature change in °F, or a coefficient in ppm/°C with a change in °C. A negative temperature change gives a negative result: the aluminum contracts.

How to Calculate Aluminum Thermal Expansion

The alloy grade matters. Aluminum alloys do not all expand at the same rate, so a generic “aluminum” figure is not reliable for a tight-tolerance fit.

The coefficients below come from the University of Chicago linear thermal expansion table. Ppm means parts per million, or millionths of the original length per degree of temperature change.

Aluminum Grade or Purity	Linear Expansion, ppm/°F	Linear Expansion, ppm/°C
Aluminum, 99.996% purity	13.1	23.6
EC 1060 and 1100	13.1	23.6
2011 and 2014	12.8	23.0
2024	12.7	22.8
2218	12.4	22.3
3003	12.9	23.2
4032	10.8	19.4
5005, 5050, and 5052	13.3	23.8
5056	13.4	24.1
5083	13.0	23.4
5086 and 5154	13.3	23.9
5357	13.2	23.7
5456	13.3	23.9
6061 and 6063	13.0	23.4
6101 and 6151	12.8	23.0
7075	12.9	23.2
7090 and 7178	13.0	23.4

Alloy-specific coefficients can vary, so a generic aluminum coefficient can produce the wrong clearance for a closely fitted part. Use the entry that matches the specified aluminum grade or purity.

Step 1: Identify the Aluminum Alloy

Look for the alloy designation on the drawing, material certificate, supplier listing, or existing part marking.
Select the corresponding coefficient from the table.
If the grade is unknown, treat the calculation as an estimate rather than using it to set a critical fit or structural movement allowance.

For an extrusion, rail, or machined part, use the grade-specific coefficient rather than a generic aluminum value.

Step 2: Establish the Starting Length and Temperature Change

Measure or use the drawing length at the known reference temperature.
Subtract that reference temperature from the expected hottest or coldest temperature.
Keep the temperature scale consistent with the coefficient you selected.

The important value is the temperature change, not the final temperature.

If a part is assembled at a hot temperature and later cools, calculate the temperature drop instead. That tells you how much the part will shorten.

Step 3: Apply the Formula

Convert ppm to a decimal before multiplying. For example, 13.0 ppm/°F is:

\[ 13.0 \div 1{,}000{,}000 = 0.0000130/\degree F \]

A 20-foot 6061 aluminum extrusion is 240 inches long. If it rises from 50°F to 130°F:

Multiply the decimal coefficient by the starting length and the temperature change.

The extrusion becomes about 1/4 inch longer.

This calculation works in feet, inches, millimeters, or meters as long as the starting length and result use the same length unit. The coefficient is a relative change, so it does not require converting between length units.

Step 4: Allow for the Calculated Movement

Use the full calculated change in length when setting end clearances, expansion joints, or sliding connections.
Decide where the part will be fixed and where it can move.
Account for the temperature at installation, because a rail installed on a hot afternoon has less room to expand but more room to contract.
Put the reference temperature, expected temperature range, alloy, and calculated movement on the drawing or job notes.

For a public handrail, a long exterior assembly, a load-bearing structure, or a system attached to another material, the connection design also needs to account for loads, code requirements, and movement of the adjoining materials.

Designing for Long Rails, Extrusions, and Joined Parts

Long runs of aluminum handrail do expand in heat. The total movement increases with length through the same temperature change.

Do not assume that fastening both ends tightly will stop the issue. It can stop visible movement at the ends, but the expanding aluminum then develops compressive stress. Depending on the geometry and support conditions, that stress may lead to bowing, buckling, loosened fasteners, noise, or damage to connected parts.

For an aluminum rail, trim, or extrusion assembly:

Establish one intentional fixed location.
Provide movement capacity at the other supports or joints where the design permits it.
Allow for movement at corners, splices, end caps, and interfaces with masonry, wood, steel, or glass.
Calculate the temperature span from the actual installation temperature to the expected hot and cold conditions.

Aluminum also expands more than typical steel for the same temperature change. An aluminum panel attached rigidly to a steel frame may move differently from its support, especially outdoors. The same issue applies to mixed-material assemblies containing stainless steel fasteners, glass, wood, or stone.

Holes expand with an aluminum part as it heats. That can slightly change the fit around a bolt, but it does not solve the larger issue of different materials moving at different rates. Connection details need to accommodate the assembly’s overall movement, not just the diameter change of one hole.

Why a Heated Aluminum Rectangle Can Warp

One common cause is a temperature gradient. Heating one side of a plate with a torch, welding along one edge, or exposing only one face to intense sunlight makes that area expand before the rest of the piece. The hotter area becomes effectively longer and can pull the sheet into a curve.

Restraint is another cause. A sheet clamped tightly on opposite sides may have no room to grow in length. As its temperature rises, compression builds in the plane of the sheet. Thin material is especially prone to buckling under this condition.

Residual stress can contribute as well. Rolled, formed, welded, or heavily machined aluminum may contain internal stresses. Local heating or removing material can redistribute those stresses and reveal a bend or twist that was not obvious before.

To reduce unwanted distortion:

Heat broad areas as evenly as practical rather than concentrating heat in one small spot.
Avoid rigidly restraining a part that must be heated.
Let a heated part return to a uniform temperature before judging whether it has permanently changed shape.
Use fixtures and welding or heating procedures appropriate to the part’s thickness, alloy, and required flatness.

How to Check Movement and Prevent Fit Problems

A calculation is most useful when it matches the real part and its real temperature conditions.

Start by recording the length between two repeatable measurement points and the part temperature at the time of measurement. Measure the same points again after the part reaches a different, uniform temperature. Compare the measured change with the calculated change.

If the part moves more or less than expected, check these items before changing the design:

Confirm the alloy and use its corresponding coefficient.
Confirm the actual temperature of the metal, not merely the surrounding air.
Check whether one portion of the part is hotter than another.
Look for clamps, fasteners, adhesive bonds, or connected materials that restrict movement.
Check whether the part is bending or bowing, which can make an end-to-end measurement misleading.

For critical work, use the certified alloy and the material producer’s engineering data for the full operating temperature range. Linear coefficients are useful design inputs, but real assemblies also respond to joint design, geometry, loads, and temperature differences across the part.

Frequently Asked Questions

Does aluminum expand when hot?

Yes. Aluminum expands when heated and contracts when cooled. Depending on alloy, aluminum changes length as its temperature changes, which can matter in long extrusions, rails, panels, and close-fitting machined assemblies.

How much does aluminum expand at 100 degrees?

“100 degrees” must mean a temperature change, not simply a final temperature. The amount of expansion depends on the temperature change, the part’s starting length, and the aluminum grade. A part sitting at 100°F has expanded only by the difference between 100°F and its starting temperature.

Do long runs of aluminum handrail expand due to heat?

Yes. A long aluminum handrail expands in direct proportion to its length and the temperature rise. A rail with no planned movement path can push on end fittings, bind at joints, bow, or place stress on anchors, so its connections need to accommodate the calculated movement.

Does aluminum stop growing at a certain temperature when hot?

No single temperature acts as a normal “stop growing” point for aluminum. It continues to change size as its temperature changes while it remains solid, although the exact expansion behavior can vary with alloy and temperature range. Before cutting or fastening a long aluminum part, identify its alloy, define its hottest and coldest expected temperatures, and calculate the movement from its installation temperature.

Does aluminum have more thermal expansion than steel?

Yes. For the same temperature change, pure aluminum is listed at 23.1 × 10⁻⁶/°C, while carbon steel is listed at 11–13 × 10⁻⁶/°C, so aluminum expands nearly twice as much. Values vary by alloy.