What this calculator does
GSM is grams per square metre, so a sheet weighs its GSM multiplied by its area. A sheet of 80 gsm A4 covers 0.0624 m² and weighs 4.99 g, which makes a 500 sheet ream 2.495 kg.
Because the A series halves in area at each step, the weights halve with it. At 80 gsm, A3 is 9.98 g a sheet, A4 is 4.99 and A5 is 2.49. The convenient consequence is that 80 gsm A4 works out at very close to 200 sheets per kilogram, which is worth remembering for postage.
The formula
The sheet area in square metres is the width multiplied by the height, both converted from millimetres. Multiplying by the GSM gives the weight of one sheet in grams, and multiplying by the sheet count gives the stack. GSM is independent of sheet size, which is what makes it comparable across formats, unlike the US basis weight system.
| Term | Meaning |
|---|---|
| GSM | Grams per square metre, the weight of a one metre square of the paper. |
| Ream | 500 sheets, the standard packaging quantity. |
| Basis weight | The US system, quoted in pounds per 500 sheets of a parent size that differs by paper type, which is why it is not comparable across types. |
| A series | ISO sizes where each step halves the area of the one before. |
The inputs explained
| Field | What to enter |
|---|---|
| Paper weight (GSM) (g/m²) | Paper weight in grams per square metre. Standard office paper is 80; letterheads are often 100 to 120; card starts around 200. |
| Sheet width (mm) | Sheet width in millimetres. A4 is 210. |
| Sheet height (mm) | Sheet height in millimetres. A4 is 297. |
| Number of sheets | Number of sheets. 500 is a ream. |
When to use it
Working out postage
Postal rates step at weight thresholds, and knowing the paper weight before adding an envelope decides which band a mailing falls into.
Comparing paper stocks
GSM is the standard basis for comparison, and the weight per sheet makes the difference between 80 and 120 gsm concrete.
Estimating a shipment
Boxes of paper are heavy, and the stack weight is what determines whether a load is within a courier limit.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does a ream weigh at each paper weight?
A range of paper weights at a fixed sheet size and count.
| Paper weight | Weight per sheet | Stack weight | Sheets per kilogram |
|---|---|---|---|
| 70 gsm | 4.37 g | 2.183 kg | 229 |
| 80 gsm | 4.99 g | 2.495 kg | 200 |
| 100 gsm | 6.24 g | 3.118 kg | 160 |
| 120 gsm | 7.48 g | 3.742 kg | 134 |
| 160 gsm | 9.98 g | 4.990 kg | 100 |
| 300 gsm | 18.71 g | 9.356 kg | 53 |
Questions
How much does a sheet of A4 paper weigh?
At the standard 80 gsm, 4.99 g. The area of an A4 sheet is 0.0624 m², so the weight is that multiplied by the GSM. At 100 gsm the same sheet is 6.24 g, and at 120 gsm it is 7.48 g.
What does GSM mean?
Grams per square metre: the weight of a one metre by one metre piece of that paper. Because it is independent of sheet size, it compares directly across formats and paper types, which is its main advantage over the US basis weight system.
How much does a ream of paper weigh?
2.495 kg for 500 sheets of 80 gsm A4, or about 5.5 lb. A box of five reams is therefore around 12.5 kg. Heavier stocks scale in direct proportion, so 120 gsm is half again as heavy.
Why is US paper quoted in pounds?
The basis weight system quotes the weight of 500 sheets of a parent size, but the parent size differs by paper type. So 20 lb bond and 50 lb text are the same weight of paper despite the different numbers, which is why GSM is the clearer measure.
For shipping weight bands, see the dimensional weight calculator. For how long a document takes to read, see the reading time calculator.