Paper Weight Calculator (GSM to KG)

GSM stands for grams per square metre (g/m²) — it's the international standard (ISO 536) measure of a paper's grammage, or mass per unit area. An A0 sheet (which by definition has an area of exactly 1 square metre) of 80gsm paper weighs exactly 80 grams.

Multiply the GSM by the sheet's area in square metres to get the weight of one sheet in grams, multiply that by how many sheets you have, then divide by 1,000 to convert grams to kilograms. This calculator does that automatically once you enter your paper size, GSM and sheet count.

80gsm is the standard weight for everyday office printer and copier paper in the UK and EU. Lighter stock (around 60–70gsm) is sometimes used for newsprint or high-volume internal drafts, while 90–100gsm is a common step-up for slightly more premium everyday printing.

A standard 500-sheet ream of 80gsm A4 paper weighs approximately 2.5kg (2.49kg from the exact calculation). Heavier stock weighs proportionally more — a ream of 100gsm A4 weighs around 3.12kg, and a ream of 120gsm A4 weighs around 3.74kg.

Enter your sheet size, the GSM of the stock you're using, and the total number of sheets in the run. The calculator gives you the total weight directly, plus the weight per sheet and per standard ream if you want to check the figures your supplier gives you.

Yes — GSM only measures density, not total weight. A larger sheet (like A3) weighs more than a smaller sheet (like A5) even at the identical GSM, simply because it has more area. This calculator accounts for your specific sheet size, not just the GSM figure.

GSM measures mass per area (density x thickness combined), while caliper measures physical thickness alone, typically in microns or points. Two papers can share the same GSM but feel different in thickness if they're made with different densities of fibre — GSM alone doesn't guarantee a specific caliper.

As general UK print-trade guidance: 80–100gsm suits everyday documents and letters, 120–170gsm suits flyers and posters that need to feel more substantial, 250–350gsm suits business cards and postcards, and booklet covers commonly use 250–300gsm with 100–150gsm text pages inside. Always check your specific printer's stock list, since exact ranges vary.

Royal Mail's Large Letter format covers items up to and including 750g, provided they also fit within the separate 353 x 250 x 25mm size/thickness limit. This calculator's postage-format result tells you which weight band your total falls into, but always check your envelope or packaging also meets the size and thickness limit for that band, since this calculator checks weight only.

Above 20kg, standard Royal Mail Medium Parcel postage no longer applies — you'd need a heavier parcel or freight/courier service instead, and it's usually worth getting a bulk quote from your supplier or a courier rather than trying to post it in multiple smaller parcels.

GSM (g/m²) is the global metric standard and is used across the UK, Europe and most of the world. The US paper trade traditionally uses "basis weight" in pounds (e.g. "20lb bond" or "24lb text"), which is not a simple unit conversion from GSM — it depends on a different reference sheet size for each paper category (bond, text, cover, etc.), so a direct GSM-to-lb comparison needs a conversion table for that specific category rather than a single multiplier. This calculator works in GSM/kg only.

Yes — the GSM-to-weight formula works the same way for card as it does for paper; card stock is simply paper with a higher GSM (typically 200gsm and above). A smart insight flags unusually light or heavy GSM values so you can confirm you've entered the figure you meant to.

It uses the standard ISO 536 grammage formula, which is exact for flat, uncoated sheet weight, so the maths itself has no margin of error. Real-world totals can differ very slightly from a supplier's stated box or ream weight due to factors like coatings, moisture content, and packaging materials (the box or wrapper itself), which this calculator does not include.

Slightly — paper is hygroscopic and can absorb a small amount of moisture from the air, which can add a small percentage to its actual weight compared to the "conditioned" GSM figure measured under standard lab humidity. This is normally a minor effect for everyday print/postage planning and isn't modelled separately by this calculator.

Because a full 500-sheet ream of standard 80gsm A4 paper weighs about 2.49kg, which is over Royal Mail's 2kg Small Parcel limit — this is a genuinely useful thing to know before assuming you can post a ream as a "small" parcel. Splitting a large order into multiple smaller parcels, or getting a bulk courier quote, is often cheaper than one large parcel once you're above the Small Parcel band.