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Paper Weight Calculator

Determine the weight of paper sheets using grammage (grams per square meter) or basis weight (pounds per ream). Whether you're ordering supplies for an office, managing print production, or comparing paper stock specifications, this calculator converts between weight systems and computes individual sheet and bulk weights across any paper size or type.

Last updated:

Creators Jasmine J. Mah, BSc
Reviewers Steven Wooding and Tibor Pál
1,053 people find this calculator helpful

Understanding Paper Grammage

Grammage represents the weight of paper expressed in grams per square meter (g/m²), commonly abbreviated as GSM. This metric standardises paper weight across manufacturers globally, appearing on packaging labels worldwide.

Grammage serves a dual purpose: it quantifies actual weight and indicates relative stiffness. A 300 GSM card stock feels substantially stiffer than 80 GSM copy paper. However, grammage alone does not determine thickness—two papers with identical grammage can vary in caliper due to differences in fibre density and coating.

Common grammage ranges include:

  • Copy and printer paper: 60–90 GSM
  • Cardstock and business cards: 250–350 GSM
  • Poster and cover stock: 200–300 GSM
  • Fine art and specialty papers: 150–400 GSM

Basis Weight and Paper Stock Types

Basis weight measures the mass of a ream (500 sheets) of paper at its standard or 'basic' sheet size, expressed in pounds. The basic size varies by stock type, creating potential confusion when comparing papers across categories.

Stock types and their reference basic sizes include:

  • Bond: 17 × 22 inches
  • Text: 25 × 38 inches
  • Cover: 20 × 26 inches
  • Tag: 24 × 36 inches
  • Index: 25.5 × 30.5 inches
  • Bristol: 22.5 × 28.5 inches

A 24 lb bond paper is entirely different from 24 lb text paper because their reference sheet sizes differ. Converting between basis weights across stock types requires accounting for these dimensional variations through a standardised conversion factor.

Paper Weight Calculation Formula

To find the weight of a single sheet, multiply its area by its grammage. For bulk quantities, multiply the per-sheet weight by the number of sheets.

Weight (g) = Length (m) × Width (m) × Grammage (GSM)

Total Weight (kg) = Weight per sheet (g) × Quantity × 0.001

Grammage (GSM) = Basis Weight (lbs) × 1406.138 / Basic Area (m²)

  • Length — Sheet length in metres
  • Width — Sheet width in metres
  • Grammage (GSM) — Weight in grams per square metre
  • Basis Weight — Weight in pounds of 500 sheets at standard size
  • Basic Area — Area of reference sheet size in square metres
  • Quantity — Number of sheets

Common Pitfalls When Calculating Paper Weight

Avoid these frequent mistakes when determining paper specifications or comparing stock options.

  1. Confusing basis weight across stock types — A 20 lb bond and 20 lb text are not equivalent weights. Always verify the stock type when comparing basis weights, as each category uses a different reference sheet size. Use a conversion calculator when switching between bond, text, cover, or other categories.
  2. Forgetting unit conversions — Mixing inches with metres or grams with kilograms leads to wildly inaccurate results. Ensure dimensions are consistently in metres before multiplying by GSM. When calculating total weight of reams, convert grams to kilograms by dividing by 1000.
  3. Assuming grammage equals thickness — Two papers with identical GSM can have different caliper (thickness) depending on how densely the fibres are compressed. A coated art paper and an uncoated text paper at 150 GSM will feel and handle differently, so grammage alone does not predict stiffness or rigidity in all contexts.
  4. Overlooking moisture content variance — Paper weight fluctuates slightly with humidity. Standard testing assumes 50% relative humidity, but paper stored in dry or humid conditions may weigh slightly more or less. For precision work, store and weigh samples under controlled conditions if accuracy beyond ±2% is required.

Worked Example: Ordering Office Supplies

Suppose your office needs five reams of 70 GSM A4 copy paper. An A4 sheet measures 210 × 297 millimetres (0.210 × 0.297 metres).

Step 1: Calculate area of one sheet.
Area = 0.210 m × 0.297 m = 0.06237 m²

Step 2: Calculate weight per sheet.
Weight = 0.06237 m² × 70 GSM = 4.3659 grams

Step 3: Calculate total weight.
Five reams = 2,500 sheets
Total weight = 4.3659 g × 2,500 = 10,914.75 g ≈ 10.9 kg

This tells you that ordering five reams of A4 paper at 70 GSM will require approximately 11 kilograms of shelf space and shipping capacity. Adjusting the grammage upward would proportionally increase the weight; 90 GSM A4 would weigh about 14.1 kg for the same five reams.

Frequently Asked Questions

How do I convert basis weight to grammage?

Multiply the basis weight in pounds by the conversion factor 1406.138, then divide by the basic area in square metres. The formula is: GSM = (Basis Weight × 1406.138) / Basic Area. For example, 20 lb bond paper with a basic area of 0.0236 m² converts to approximately 50 GSM. This conversion accounts for the different reference sheet sizes used by each stock type.

Why do different paper types have different basic sizes?

Historical printing practices established different 'basic' or 'parent' sheet sizes for bond, text, cover, and other categories based on common use cases and manufacturing equipment. Bond paper's 17 × 22 inch basic size suited letterhead production, while cover stock's 20 × 26 inch size worked well for envelopes. These standards persist to ensure consistency across the industry, even though modern cutting and trimming can start from any size.

What is the relationship between GSM and paper thickness?

GSM and thickness (caliper) are not directly linked. Paper density varies significantly depending on fibre type, coating, and manufacturing process. A 150 GSM glossy coated art paper may be thinner than 150 GSM uncoated text because coating adds weight without proportionally increasing thickness. For precise thickness requirements, always check the caliper specification separately from grammage.

How accurate is this calculator for non-standard paper sizes?

The calculator works accurately for any rectangular sheet as long as you input precise dimensions. The formula (length × width × GSM) is universal and does not depend on standard sizes. Custom-cut papers, envelopes, and irregular sizes all calculate correctly provided you measure or know the exact dimensions in metres or inches.

Does paper weight change with humidity or storage conditions?

Yes, paper is hygroscopic and absorbs moisture from air. Weight can fluctuate 2–3% between 30% and 70% relative humidity. Paper manufacturers test and specify weights at 50% humidity as a standard. For most office and printing purposes, this variance is acceptable, but if your application requires precision—such as weight-sensitive mail sorting or quality control—store samples in controlled conditions and test accordingly.

What is a typical weight for standard office copy paper?

Standard office copy paper is typically 75–80 GSM or 20 lb bond equivalent. An 80 GSM letter-size sheet (8.5 × 11 inches) weighs approximately 4.5 grams. A full ream of 500 sheets at this weight is roughly 2.25 kilograms. Premium or heavier stock for presentations or brochures ranges from 100–160 GSM, while lightweight airmail or onionskin paper may be 35–50 GSM.

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