Typical densities (common units)
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Borosilicate glass (e.g., Borosilicate 3.3) — ≈ 2.23 g/cm³ (≈ 2,230 kg/m³). This is the standard for chemical/pressure-rated sight glasses.
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Soda-lime (float) glass — ≈ 2.5–2.53 g/cm³ (≈ 2,500–2,530 kg/m³). Common for less demanding sight windows and many tempered sight glasses.
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Fused silica / fused quartz — ≈ 2.20–2.23 g/cm³ (≈ 2,200–2,230 kg/m³). Use it in applications that must have very low thermal expansion or high optical quality.
Note: Sight-glass product datasheets may show different numbers (like 2.23 vs. 2.49 g/cm³). This can happen due to glass formulation, tempering, or testing methods. Always use the supplier’s declared density for accurate mass or weight calculations.
Why density matters for gauge glass (practical implications).
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Weight & shipping — density × volume = mass; choosing the correct density avoids underestimating freight costs.
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Mechanical support—heavier glass adds more load to frames and flanges. So, structural checks might need the right material density.
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For buoyancy or float systems, use real density in mass and center-of-gravity calculations. This is important if a float or indicator touches the glass assembly. For all engineering checks, use the exact density from the supplier’s datasheet. Don’t use rounded textbook values.
How to specify density in an RFQ or drawing.
When you request a quote or send drawings, include:
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Glass type (e.g., “Borosilicate 3.3” or “Tempered soda-lime sight glass”).
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Thickness (mm) and dimensions (Ø or length × width).
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Any tempering or heat treatment can slightly alter the density values in datasheets.
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Required certificates (material test report, DIN/ISO references). Doing this allows the supplier to give you an exact mass per part rather than an estimate.
Quick conversion table (for convenience)
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1 g/cm³ = 1,000 kg/m³.
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Borosilicate 3.3: 2.23 g/cm³ = 2,230 kg/m³.
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Soda-lime: ≈ 2.50 g/cm³ = 2,500 kg/m³.
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Fused silica: ≈ 2.20 g/cm³ = 2,200 kg/m³.
Short worked example.
A circular sight glass disc, 100 mm in diameter and 6 mm thick:
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Volume = π × (0.05 m)² × 0.006 m ≈ 4.712 × 10⁻⁵ m³.
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Mass (borosilicate 2,230 kg/m³) ≈ 0.105 kg (≈ 105 g). Use the supplier’s density for final packing/handling numbers.
Final recommendations (what to do next)
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Always ask for the supplier’s material datasheet. It often includes density, tolerance, and test method. These are the official values for engineering.
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Use borosilicate (3.3) glass or the specified tempered glass for high-pressure and temperature needs. The density differences are minor, but other mechanical and thermal properties vary more.
References (selected authoritative sources)
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Borosilicate 3.3 technical datasheets and manufacturer pages (density ≈ 2.23 g/cm³).
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Soda-lime / float glass property listings (density ≈ 2.5 g/cm³).
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Comparative material tables (fused silica ≈ 2.20–2.23 g/cm³).
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Sight-glass product datasheets (manufacturer-measured densities, tempered vs. untreated).
