Paper grammage and thickness
Convert paper grammage to thickness and back with thickness (μm) = grammage (g/m²) ÷ apparent density (g/cm³): offset 80 g/m² ≈ 100 μm, coated 80 g/m² ≈ 80 μm, plus A4 sheet weight, ream weight and a 70/80/100/128 g/m² reference table of empirical values.
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Conversion result
Apparent densities are industry estimates within ±15%.
Enter a grammage or thickness to convert
Grammage: 0 · Thickness: 0 · Per A4 sheet: 0
What this tool does
- Check paper thickness before designing a book to estimate spine width and binding.
- Cost print jobs and freight: ream weight × reams gives tonnes, A4 weight covers postage.
- Audit a supplier claim such as “80 g coated at 100 μm” by back-computing the bulk.
Example
Input
128
Output
铜版纸（涂布）（表观密度 1 g/cm³）：128 g/m² ≈ 128 μm 换算公式：厚度(μm) = 克重(g/m²) ÷ 密度(g/cm³) 每张 A4（210 × 297 mm）重量：7.98336 g 每令 500 张全开（787 × 1092 mm）重量：55.001856 kg 常用克重对照：70 g/m² ≈ 70 μm、80 g/m² ≈ 80 μm、100 g/m² ≈ 100 μm、128 g/m² ≈ 128 μm 提示：表观密度按行业松厚度经验值取值，同克重不同厂家可差 15%，精确厚度请用千分尺实测。
Offset paper at 80 g/m² uses an apparent density of 0.8 g/cm³, giving 100 μm and about 4.99 g per A4 sheet.
Frequently asked questions
Where does the formula come from?
Grammage is mass per square metre; with thickness t (μm) the volume of 1 m² is 10000 × t(cm) cm³, so mass = volume × density simplifies to t(μm) = grammage(g/m²) ÷ density(g/cm³).
Is 80 g paper 80 μm or 100 μm?
It depends on the grade. Coated art paper is calendered to about 1.0 g/cm³, so 80 g is roughly 80 μm; offset paper is bulkier at about 0.8 g/cm³, giving about 100 μm. That is why equal grammages feel different.
Is apparent density the same as real density?
No. Paper is porous, so apparent density (the inverse of bulk) includes the air between fibres. Cellulose itself is about 1.5 g/cm³ while paper sits at 0.6–1.1 g/cm³. The value here is only for thickness conversion.
How accurate is it?
It is an industry estimate within about ±15%. The same 80 g offset sheet can be 98 μm from one mill and 104 μm from another. For exact figures measure several points with a micrometer.
How is the ream weight derived?
One ream is 500 sheets of 787 × 1092 mm: grammage × 0.787 × 1.092 × 500 ÷ 1000 kg. An 80 g offset ream works out at about 34.38 kg, which matches a scale.
How do I convert to pounds?
US practice quotes ream weight in pounds for 25 × 38 inch sheets, which is awkward. Roughly, 80 g/m² is about 20 lb bond or 55 lb text. Always confirm with the mill; g/m² is the safest unit.
Keywords：纸张克重纸张厚度paper thicknessgsm 换算松厚度铜版纸A4 重量纸张开料