Three free tools in one, nothing stored, all in your browser. Convert US basis-weight pounds (LBS) to GSM and back across all four paper grades (Bond, Text, Cover, Tag), convert caliper points (pt) to millimeters, mils, and microns, and calculate the total weight of a cardboard sheet or box blank in grams and pounds for freight estimates.
Why three tools? Because paper weight is three different measurements that packaging buyers mix up constantly: GSM (grams per square meter — how heavy per area), LBS basis weight (pounds per ream of a parent-size sheet — the US system, with 4 different parent sizes), and caliper in points (thickness, where 1 pt = 0.001 inch). This page converts all three cleanly, then lets you compute total weight of a run for shipping-cost estimates.
Pick your paper grade (parent-sheet class), enter one value, get the other. The parent class is the critical input — "80 lb Cover" (216 GSM) and "80 lb Text" (118 GSM) are the same number but different weights.
Edit either LBS or GSM — the other updates automatically. Change the paper grade dropdown to see how the same pound number maps to different GSM values across grades.
Thickness, not weight. 1 point (pt) = 1 mil = 0.001 inch = 0.0254 mm = 25.4 microns. Edit any one field, the other three recalculate.
Common paperboard calipers: 14 pt (light cosmetics), 16 pt (standard cosmetics / supplements), 18-20 pt (medium retail), 22-24 pt (heavier bottles / e-commerce), 28+ pt (premium retail).
Enter the sheet (or flat box-blank) dimensions and quantity. We compute total weight for freight estimates. Formula: weight (g) = GSM × sheet area in m² × number of sheets.
Freight tip: dividing total weight by number of pallets gives you per-pallet weight for freight-class and shipping-cost estimates. US LTL freight is priced by weight + class, so GSM × sheet count directly affects the number.
Need the actual board? We cut custom plain cardboard boxes and printed cardboard boxes at any GSM/caliper spec with no die, plate, or setup fees. See all stock options on our packaging materials page, and read the deep-dive at our cardboard weight GSM calculation guide.
Reference values across the four US parent-sheet classes. GSM is unambiguous; LBS requires knowing the grade.
| GSM | Bond / Writing (lb) | Text / Book (lb) | Cover (lb) | Tag / Bristol (lb) |
|---|---|---|---|---|
| 60 | 16 | 41 | 22 | 27 |
| 75 | 20 | 51 | 28 | 34 |
| 90 | 24 | 61 | 33 | 41 |
| 104 | 28 | 70 | 38 | 47 |
| 118 | 31 | 80 | 44 | 54 |
| 148 | 39 | 100 | 55 | 67 |
| 176 | 47 | 119 | 65 | 80 |
| 216 | 58 | 146 | 80 | 99 |
| 270 | 72 | 182 | 100 | 123 |
| 325 | 86 | 220 | 120 | 148 |
| 400 | 106 | 270 | 148 | 182 |
| 500 | 133 | 338 | 185 | 228 |
GSM and caliper don't convert directly (bulk density varies by stock), but these are the pairings packaging buyers see most often on quote sheets.
| Caliper | mm | Typical GSM (SBS) | Typical use |
|---|---|---|---|
| 12 pt | 0.30 | 230-260 | Business cards, light inserts |
| 14 pt | 0.36 | 280-310 | Light cosmetics, tea sachets, small food |
| 16 pt | 0.41 | 320-350 | Standard cosmetics, supplements |
| 18 pt | 0.46 | 350-385 | Medium retail, bottle neckers |
| 20 pt | 0.51 | 385-420 | Standard bottles, mid-retail |
| 22 pt | 0.56 | 420-460 | Heavier bottles |
| 24 pt | 0.61 | 460-500 | E-commerce cartons, heavier retail |
| 28 pt | 0.71 | 500-560 | Premium retail, luxury folding cartons |
| 32 pt | 0.81 | 560-640 | Heavy-duty, structural |
GSM from LBS: GSM = (basis weight in pounds × 1406.5) ÷ parent sheet area in square inches. The 1406.5 constant comes from unit conversion: (453.592 g/lb × 1550.0031 in²/m²) ÷ 500 sheets per ream = 1406.5. The parent sheet area depends on grade — this is why the dropdown matters.
Caliper to mm: 1 point = 1 mil = 0.001 inch, and 1 inch = 25.4 mm, so mm = points × 0.0254. Microns are mm × 1000, so microns = points × 25.4.
Total cardboard weight: weight in grams = GSM × sheet area in m² × number of sheets. Convert inches to meters first (1 in = 0.0254 m), multiply L × W for area in m², then multiply by GSM and sheet count. Divide by 453.592 to get pounds.
GSM = (basis weight in pounds × 1406.5) ÷ parent sheet area in square inches. US paper weight is basis weight — the weight of 500 sheets of a parent-size uncut sheet, and the parent size differs by paper grade: Bond/Writing is 17×22 in (374 sq in), Text/Book/Offset is 25×38 in (950 sq in), Cover is 20×26 in (520 sq in), Tag/Index/Bristol is 22.5×28.5 in (641.25 sq in). So 20 lb Bond = 75 GSM, 70 lb Text = 104 GSM, 80 lb Cover = 216 GSM. Picking the wrong parent class is the #1 trap in paper weight conversion — "80 lb Cover" and "80 lb Text" are the same number but different weights.
GSM stands for grams per square meter — the weight of a 1-meter-by-1-meter sheet of paper. GSM is the ISO 536 global standard because it's unambiguous: one square meter is one square meter everywhere, so a 300 GSM board is 300 GSM whether it's cut as a business card or a cereal box. US "basis weight" pounds requires knowing the parent-sheet class, which creates ambiguity.
GSM measures mass per area (grams per square meter — how heavy). Points and mils measure thickness (how thick): 1 point (pt) = 1 mil = 0.001 inch = 0.0254 mm = 25.4 microns. A 20 pt board is 0.020 inch thick (0.508 mm). GSM and caliper don't convert directly to each other because bulk (density) varies by paper type — a 300 GSM board can be 18 pt (dense SBS) or 24 pt (bulky kraft). Both numbers matter: GSM drives shipping cost, caliper drives structural feel.
Total weight in grams = GSM × sheet area in m² × number of sheets. Convert sheet dimensions from inches to meters first (1 inch = 0.0254 m), then multiply L × W to get area in m². For a 20×30 in sheet in 300 GSM: area = 0.508 × 0.762 = 0.387 m², weight per sheet = 300 × 0.387 = 116 g = 0.256 lb. For 1,000 sheets: 256 lb total. Use this to estimate freight weight on bulk cardboard runs before shipping.
Common caliper and GSM ranges by use: 14 pt (280-310 GSM SBS) for light cosmetics and tea boxes; 16 pt (320-350 GSM) standard cosmetics and supplements; 18-20 pt (350-410 GSM) medium retail and bottles; 22-24 pt (430-500 GSM) heavier bottles and e-commerce cartons; 28+ pt (500+ GSM) premium retail cartons. Rigid chipboard runs 1.5-3 mm (not usually spec'd in GSM). Corrugated is spec'd by flute (E/B/C) and ECT rating, not GSM.