Cardboard Thickness Guide: Flute Sizes, ECT and Board Grades
By the Avco Boxes team · Updated
Corrugated cardboard thickness depends on its flute size. F flute is about 1/32 inch (0.8 mm), E flute about 1/16 inch (1.6 mm), B flute about 1/8 inch (3.2 mm), C flute about 5/32 inch (4 mm) and A flute about 3/16 inch (4.8 mm). Double wall board is roughly 1/4 inch thick. Thin paperboard, like a cereal box, is measured in points instead.
Cardboard is really two different materials
"Cardboard" is an everyday word for two materials that are measured differently. Corrugated board has a wavy middle layer, the fluting, glued between flat liners. It is what shipping boxes and pizza boxes are made of, and its thickness comes from the size of the flutes. Paperboard is a single thick sheet with no fluting. Cereal boxes, many bakery boxes and sub boxes are paperboard, and it is measured in points.
When people ask how thick cardboard is, they usually mean corrugated board, so most of this guide covers flute sizes.
Corrugated flute sizes chart
| Flute | Thickness (inches) | Thickness (mm) | Typical uses |
|---|---|---|---|
| F flute | about 1/32 | about 0.8 | Small retail boxes, fast-food clamshells |
| E flute | about 1/16 | about 1.6 | Pizza boxes, retail and display boxes, printed mailers |
| B flute | about 1/8 | about 3.2 | Pizza boxes for delivery, die-cut boxes, canned goods cases |
| C flute | about 5/32 | about 4 | Standard shipping cartons, the most common box flute |
| A flute | about 3/16 | about 4.8 | Cushioning and stacking where extra thickness matters |
Exact thickness varies a little between mills and with the weight of the liners, so treat these as working figures rather than a specification. The letters are historical: they name the flutes in the order they were introduced, not from thinnest to thickest.
Single wall, double wall and triple wall
- Single wall: one layer of fluting between two liners. Most food packaging, including pizza boxes, is single wall.
- Double wall: two layers of fluting and three liners, usually combined as BC flute. It is roughly 1/4 inch (about 6–7 mm) thick and is used for heavy shipping and stacking.
- Triple wall: three layers of fluting, around 1/2 inch thick. It is used for bulk bins and very heavy industrial loads.
Thickness vs strength: ECT and burst ratings
Thicker board is not automatically stronger. Strength also depends on the weight of the liners and fluting paper, and boxes are rated with two common tests.
- Edge Crush Test (ECT): how much force the board takes on its edge before crushing, in pounds per inch. It predicts stacking strength. 32 ECT is a common single wall grade; 44 ECT is a heavier single wall, and double wall boxes are often 48 ECT or higher.
- Burst (Mullen) test: how much pressure punctures the board, in pounds per square inch. It relates to rough handling. 200 lb is a common single wall rating.
Shipping boxes often carry a printed box maker's certificate on a bottom flap that states the rating. For a food box, the rating matters less than whether the flute and board suit the food and the trip.
Paperboard thickness: points
Paperboard is measured in points, where 1 point equals 0.001 inch. A 20 point board is 0.020 inch thick, about half a millimeter. That is thinner than any corrugated flute, which is why paperboard suits lighter items such as pastries, sandwiches and cereal, and why it gives a smooth, bright surface for printing.
If you are comparing paper rather than board, our paper GSM guide explains paper weight.
Which thickness for food packaging
- Pizza boxes: E or B flute. Our corrugated pizza box comes in both. B flute (about 1/8 inch) resists crushing better for delivery, stacking and heavy deep-dish pies. E flute (about 1/16 inch) has a smoother face for printing and takes less storage space.
- Catering: a full steam pan of lasagna is heavy, so our catering cases and trays use heavy-duty corrugated board.
- Subs and pastries: lighter food suits paperboard. Our hero boxes are clay-coated paperboard, which prints crisply and resists grease spotting.
Frequently asked questions
- How thick is cardboard?
- Single wall corrugated cardboard is usually between about 1/32 inch (F flute) and 3/16 inch (A flute). The most common shipping box flute, C flute, is about 5/32 inch, or 4 mm. Double wall board is about 1/4 inch.
- How thick is a pizza box?
- Most corrugated pizza boxes use E flute (about 1/16 inch) or B flute (about 1/8 inch). B flute is thicker and better for delivery and stacking; E flute prints more smoothly.
- What is the thickest cardboard?
- Triple wall corrugated board, at around 1/2 inch, is the thickest common grade. Among single wall flutes, A flute is the thickest at about 3/16 inch.
- What does 32 ECT mean?
- The board withstands 32 pounds of force per inch of edge before crushing in the Edge Crush Test. It is a common rating for single wall shipping boxes.