Mathematics calculator

Paper Weight Calculator

Estimate paper grammage in grams per square metre from reel mass, paper length, and reel width.

Calculator inputs

Enter your values

GSM
Calculated output

Result summary

Your result will appear here

Complete the required fields and select the calculate button.

A paper reel unrolling to show length and width used to calculate area
Subtract the core and packaging mass when possible so the entered weight represents paper only.

Table of Contents

1

What is Paper Weight?

The Paper Weight Calculator estimates grammage, commonly written GSM or g/m², from the mass and dimensions of a paper reel. Grammage is the mass of paper per square metre and provides a useful way to compare stocks with different widths and lengths.

The calculation assumes the entered mass belongs to the paper represented by the full entered area. A reel core, wrapper, damaged layers or an estimated length can bias the answer. For an official product specification, use the manufacturer’s measured grammage.

2

How to Use This Calculator

  1. Enter the paper mass in kilograms. If the scale includes the core or packaging, subtract those masses first when known.
  2. Enter the paper length in metres and reel width in centimetres. The page converts width from centimetres to metres.
  3. Select Calculate. It finds area as length times converted width, converts kilograms to grams, divides mass by area, and rounds GSM to the nearest whole number.
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Formula Used

Width in metres = width in centimetres ÷ 100

Area = length in metres × width in metres

GSM = paper mass in grams ÷ area in square metres

Since kilograms are converted to grams, GSM = weight in kg × 1,000 ÷ (length in m × width in m).

4

Variables Explained

TermMeaning on this page
WeightMass of the paper reel in kilograms, ideally excluding its core and packaging.
LengthTotal paper length represented by the entered mass, in metres.
WidthReel width in centimetres; the page divides it by 100.
AreaLength multiplied by width after both are expressed in metres.
GSMGrams per square metre, rounded to a whole number for display.
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Worked Example

Take a paper-only mass of 10 kg, a length of 1,000 m and a width of 10 cm. The width is 10 ÷ 100 = 0.10 m.

Area = 1,000 × 0.10 = 100 m². Mass = 10 × 1,000 = 10,000 g. GSM = 10,000 ÷ 100 = 100 g/m², displayed as 100.

If a 1 kg core were included in the 10 kg scale reading, the paper mass would be 9 kg and the estimate would be 90 g/m² instead. This shows why tare mass matters.

6

Why Use This Calculator?

A result near a supplier’s nominal GSM can support an inventory check, but agreement does not prove the reel dimensions or mass are exact. Paper moisture, scale resolution, length estimation and manufacturing tolerance can all contribute to a difference.

A heavier GSM means more mass for the same surface area. It does not by itself specify caliper, stiffness, opacity, finish or strength because fibres and manufacturing methods differ. Compare those properties separately when choosing stock for printing or packaging.

The displayed whole number is appropriate only when the inputs justify that precision. Keep source measurements and any core deduction with the result. If a contract depends on grammage, follow the sampling and test method required by the parties rather than relying on a reel-level estimate alone.

For a better estimate, use a scale appropriate to the reel mass and measurements taken from the same reel state. A width printed on a label may be reliable, while remaining length may be only an equipment estimate. The least certain input often limits how confidently the final whole-number GSM can be used.

Grammage can also be checked from a smaller sample when an agreed test procedure is available: measure a known area and weigh it accurately. That method has its own sampling and conditioning requirements. Do not assume a small offcut represents an entire reel if coating or moisture varies across the stock.

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Common Mistakes

  • Entering width in millimetres when the form expects centimetres makes the calculated GSM ten times too small.
  • Including the reel core in paper mass makes grammage too high.
  • Using the remaining length with the original full-reel mass mixes measurements from different states.
  • Reading GSM as thickness is incorrect; papers with equal grammage can have different caliper.
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Frequently Asked Questions

What does GSM mean?

GSM means grams per square metre. It describes how much a square metre of the paper would weigh, based on mass divided by surface area.

Should the reel core be included in weight?

No, not when the aim is paper grammage. Subtract the known core and packaging mass so the numerator represents the paper spread across the entered area.

Why is width entered in centimetres?

That is the unit used by this form. The calculation converts centimetres to metres so width and length can produce square metres.

Why is the result rounded to a whole number?

The page displays the nearest whole GSM. That is convenient for common stock descriptions, though it does not make imprecise input measurements more accurate.

Is GSM the same as paper thickness?

No. GSM measures mass per area, while thickness measures distance between surfaces. Fibre, coating and compression can give papers with the same GSM different thicknesses.

Can I use the current reel weight with its original length?

Only if the mass and length describe the same amount of paper. For a partly used reel, use its remaining paper mass and remaining length together.

Why does my estimate differ from the label?

Check core mass, width units, remaining length and scale accuracy. Moisture, production tolerance and rounding can also cause a modest difference.

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Sources & References