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lb/in³ to g/cm³

1 Pound per Cubic Inch (lb/in³) = 27.6799Gram per Cubic Centimeter (g/cm³)

By KAMP Inc. / UnitOwl · Last reviewed:

Result
27.6799 g/cm³
1 lb/in³ = 27.6799 g/cm³
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How Many g/cm³ in a lb/in³?

One pound per cubic inch (lb/in³) equals approximately 27.6799 grams per cubic centimeter (g/cm³). To convert lb/in³ to g/cm³, multiply the lb/in³ value by 27.6799. The lb/in³ unit is primarily used in American manufacturing, machining, and materials engineering for metals and dense materials. Steel is about 0.284 lb/in³ (7.85 g/cm³), aluminum is 0.098 lb/in³ (2.71 g/cm³), and copper is 0.323 lb/in³ (8.94 g/cm³). Machinists calculating the weight of metal parts, manufacturing engineers selecting materials, and procurement specialists comparing material datasheets from US and international suppliers all need this conversion. The lb/in³ values are small decimals for most materials, which is why metric g/cm³ is often preferred — it produces more readable numbers. This conversion becomes especially important when a US drawing package, quote, or vendor sheet is written in inch-pound units but the analysis team or overseas supplier expects metric material properties. A unit slip here can distort part-weight estimates, shipping quotes, and even machine load assumptions for heavy components. It is also a routine checkpoint when converting material tables for ERP, CAD, or quoting systems.

How to Convert Pound per Cubic Inch to Gram per Cubic Centimeter

  1. Start with your density value in lb/in³.
  2. Multiply the lb/in³ value by 27.6799 to get g/cm³.
  3. For example, 0.284 lb/in³ x 27.6799 = 7.86 g/cm³ (steel).
  4. For a rough estimate, multiply lb/in³ by 27.7.
  5. To get kg/m³ instead, multiply lb/in³ by 27,679.9.

Real-World Examples

A material datasheet lists titanium at 0.163 lb/in³. Convert to g/cm³.
0.163 x 27.6799 = 4.51 g/cm³. Titanium is about 57% as dense as steel, which is why it is valued in aerospace.
Brass density is 0.308 lb/in³. What is that in g/cm³?
0.308 x 27.6799 = 8.53 g/cm³.
A plastic component is made from nylon at 0.041 lb/in³. Convert to g/cm³.
0.041 x 27.6799 = 1.13 g/cm³. Nylon is slightly denser than water.
Lead is listed at 0.410 lb/in³. Express in g/cm³.
0.410 x 27.6799 = 11.35 g/cm³. Lead's high density makes it useful for radiation shielding and ballast.

Quick Reference

Pound per Cubic Inch (lb/in³)Gram per Cubic Centimeter (g/cm³)
127.6799
255.3598
5138.4
10276.799
25691.998
501,384
1002767.99

History of Pound per Cubic Inch and Gram per Cubic Centimeter

The lb/in³ unit became standard in American metalworking because machinists think in inches — parts are dimensioned in inches, volumes are calculated in cubic inches, and weights are in pounds. When a machinist needs to estimate the weight of a turned part, knowing that steel is 0.284 lb/in³ lets them multiply part volume (in in³) directly by density to get weight in pounds. This practical workflow kept lb/in³ alive in American manufacturing even as international materials science standardized on g/cm³. The conversion factor of 27.6799 reflects the combined inch-to-centimeter (2.54 exactly) and pound-to-gram (453.592) relationships: 453.592 / 2.54³ = 453.592 / 16.387 = 27.6799.

Common Mistakes to Avoid

  • Confusing lb/in³ with lb/ft³. 1 lb/in³ = 1,728 lb/ft³ (12³). Steel at 0.284 lb/in³ = 490 lb/ft³. If you see a density of 490 and assume lb/in³, you will calculate a mass 1,728 times too large.
  • Using the reciprocal conversion factor. To go from g/cm³ to lb/in³, divide by 27.68 (not multiply). Steel at 7.85 g/cm³ / 27.68 = 0.284 lb/in³.
  • Not checking units on material datasheets. American datasheets may list density in lb/in³ or lb/ft³ depending on the application. Always verify which cubic unit is being used.
  • Using a nominal handbook density when alloy, porosity, or composition changes the actual value. Castings, powder-metal parts, foamed plastics, and different aluminum or brass alloys can vary enough that the conversion is correct but the chosen source density is still not appropriate for a final weight estimate.
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Frequently Asked Questions

Why do machinists prefer lb/in³ over lb/ft³?
Because machined parts are dimensioned in inches. A shaft that is 2 inches in diameter and 6 inches long has a volume of pi x 1² x 6 = 18.85 in³. Multiplying by 0.284 lb/in³ gives 5.35 lb — the weight calculation is direct and requires no unit conversions. Using lb/ft³ would require converting cubic inches to cubic feet first.
What are common metal densities in both units?
Steel: 0.284 lb/in³ = 7.85 g/cm³. Aluminum: 0.098 lb/in³ = 2.71 g/cm³. Copper: 0.323 lb/in³ = 8.94 g/cm³. Titanium: 0.163 lb/in³ = 4.51 g/cm³. Brass: 0.308 lb/in³ = 8.53 g/cm³. Cast iron: 0.260 lb/in³ = 7.20 g/cm³.
How do I estimate the weight of a machined part?
Calculate the part volume in cubic inches (using dimensions from the drawing), then multiply by the material density in lb/in³. For a steel cylinder 4 inches in diameter and 10 inches long: volume = pi x 2² x 10 = 125.7 in³, weight = 125.7 x 0.284 = 35.7 lb.
When should I convert lb/in³ to g/cm³ instead of kg/m³?
Use g/cm³ when you are comparing material datasheets, chemistry references, or international supplier specs, because that unit is common for solid materials. Convert to kg/m³ when you need the density for SI engineering calculations, simulations, or reports that standardize on meter-based units.
Why are lb/in³ values so small for most metals?
Because a cubic inch is a relatively small volume. Even a dense metal such as steel only weighs about 0.284 lb per cubic inch. Switching to g/cm³ or kg/m³ gives larger, easier-to-scan numbers, which is one reason metric density units are often preferred for material property tables.
Quick Tip

For quick metal weight estimates in a machine shop: steel is about 0.28 lb/in³, aluminum is about 0.10 lb/in³ (roughly one-third of steel), and copper is about 0.32 lb/in³. These three values cover most common machining materials and are easy to remember.

Sources & References