How to crochet a T-shirt yarn bag from a rectangular base

Who is this technique for?

The rectangular base is ideal if you want:

• A bag with good capacity (it holds more than a round base of the same width).
• A stable result: T-shirt yarn tends to “ask for shape,” and the rectangular base helps.
• Versatile styles: tote, shoulder bag, envelope bag, mini bag…

If you would like to see other constructions (round or oval bases, or a bag crocheted in one piece), we explain them in the main guide: see all the ways to crochet a bag .

Recommended materials

Essentials

• T-shirt yarn (preferably with an even thickness so the base stays regular).
• Crochet hook suitable for the thickness of the T-shirt yarn (as a reference, 8–10 mm usually works well with T-shirt yarn).
• Stitch marker to mark the beginning of the round.
• Scissors and a tapestry needle for finishing.

Optional finishing touches for a “pro” look

• Rigid base (plastic canvas, thin PVC or a purchased base) to help the bag keep its shape.
• Handles (adjustable shoulder strap, handles, rings, lobster clasps).
• Lining (cotton fabric or lightweight canvas) if you want more security and structure.
• Closure: magnetic button, zip, clasp, flap…

How to calculate the measurements of the rectangular base

Before crocheting, decide on the bag type and translate that into measurements:

Approximate measurements by style

• Mini bag / envelope bag: base 18–22 cm (length) × 6–8 cm (width).
• Medium crossbody bag: base 24–28 cm × 8–10 cm.
• Tote / roomy handbag: base 30–36 cm × 10–12 cm.

Quick rule for a “nice proportion”

A rectangular base usually looks balanced when the length is ~2.5–3 times the width. For example: 27 × 9, 30 × 10, 33 × 11…

Step by step: crocheting the rectangular base

The classic rectangular base is made as follows: make a chain, then crochet around that chain, increasing at the ends to form the rounded “curves” of the corners. With T-shirt yarn, the single crochet works especially well for a compact, stable base.

1) Start the foundation chain (the length measurement)

1. Make a chain that gives you the desired length for the base (not counting the height of the stitch).
2. As a reference, measure the chain flat on the table to check the centimeters.

2) Round 1: crochet one side, increase at the end, and return along the other side

1. Crochet single crochets along the chain (one in each chain stitch).
2. In the last chain stitch, crochet 3 single crochets in the same place (this forms the first “corner”).
3. Turn your work and crochet single crochets along the other side of the chain, working into the chain “spaces.”
4. When you reach the other end, crochet 3 single crochets into the same stitch (the second corner).
5. Join with a slip stitch if you’re crocheting in the round, or continue in a spiral, marking the beginning of the round.

3) Rounds 2 onward: increases only at the corners

Here’s the secret to keeping the base flat: increase only at the corners. Crochet the sides “normally,” and distribute the increases at each corner.

• Easy option (very common): at each corner, increase by crocheting 3 stitches into the center stitch of the corner on every round.
• More refined option (distributed): at each corner, distribute the increases: for example, in the curved section, crochet (2 stitches in 1) + 1 + (2 stitches in 1).

The important thing is that the base should remain flat when placed on the table. If it ripples, there are too many increases. If it arches like a “bowl,” there aren’t enough increases.

4) When do I stop increasing?

Stop when your base reaches the width you want (8 cm, 10 cm, 12 cm…). The length is determined by the starting chain: the base mainly grows in width with each round.

Lift the sides without letting the base open up

Once the base has reached the right size, it’s time to “build upward.” This step determines whether the bag looks firm or opens up and loses its shape.

Option A: transition round in the back loop only (BLO)

Crochet one full round of single crochet worked through the back loop only. This creates a neat fold and lifts the side wall. It is one of the most effective techniques for working with T-shirt yarn.

Option B: slip-stitch round

A round of slip stitches also creates a very defined edge (and reinforces it), but it can be stiffer.

Next: straight sides

From there, crochet in the round (or in a spiral) without increases to build height. For a medium-sized bag, 18–22 cm high usually works well, but the style is what matters here.

How to shape the bag (straight, trapezoid, envelope)

Straight “box” style bag

The simplest option: after the transition round, crochet straight sides without increases or decreases. The result is a stable, highly practical bag.

Trapezoid-style bag (wider at the bottom, narrower at the top)

To narrow it, make decreases distributed every X rounds (for example, 4 decreases per round, every 2–3 rounds), always symmetrically (front/back/sides).

Envelope-style bag (shorter, with a flap)

Crochet fewer rounds in height and finish with a firm round. The flap can be a separate piece or an extension of the back panel. 

Tips for more structure (rigid base, reinforcements)

Rigid base inside

If your bag will carry weight (phone, wallet, keys…), a rigid base makes all the difference. You can:

• Cut a base (plastic canvas/thin PVC) to the exact size and place it inside.
• Cover it with fabric so it does not rub against the T-shirt yarn.
• Secure it with a few hand stitches or by fitting it in place with the lining.

Reinforcing the top edge

To keep it from opening, finish with 1–2 firmer rounds (tight single crochet or slip stitch) and, if the bag calls for it, add a cord or ribbon inside.

Handles: where to place them and how to attach them (tote and shoulder bag)

Handles are “half aesthetics and half engineering.” A beautiful bag can be uncomfortable if the handle is not positioned or secured properly. 

Shoulder strap (long handle)

• Placement: it usually works best on the sides, slightly below the top edge (1–2 cm).
• Attachment: with rings and a lobster clasp, or sewn on with reinforcement (several firm passes).
• Tip: if the bag is heavy, add a small reinforcement piece inside (a strip of sturdy fabric or leather).

Hand handles (tote)

• Placement: front and back, centered, leaving enough room so the bag does not “close” when you pick it up.
• Attachment: ideally with hardware (rings), or with reinforced stitching plus an inner piece.

Closure and lining: when are they worth it?

Easy closures

• Magnetic snap: quick and neat, ideal for a tote.
• Button + loop: very attractive on an envelope-style bag.
• Zipper: more laborious, but provides complete security.

Lining: yes or no?

If the stitches are very open or the bag will hold small items, lining it is highly recommended. It also helps the bag keep its shape.

Professional finishing touches

• Neat finishing: hide the ends inside with a yarn needle, following the direction of the stitches.
• Firm top edge: work 1–2 tighter rounds so it doesn’t stretch.
• Label: if you’re using a sewn-on label, attach it before adding the lining to hide the inner seams.
• Gentle blocking: with T-shirt yarn, it’s usually enough to shape it by hand and let it rest, without using too much water.

Common mistakes and how to avoid them

1) The base ripples

This is usually caused by too many increases at the corners. Solution: reduce the increases on the next round or distribute them more evenly.

2) The base turns into a bowl

There aren’t enough increases (or you’re crocheting too tightly). Solution: add increases at the corners on the next round or loosen your tension.

3) The sides “flare out” and the bag loses its shape

A transition round is missing (BLO or slip stitches), or the top edge is too loose. Solution: add a transition and reinforce the edge.

4) The bag leans or becomes misshapen to one side

This happens when the decreases/increases aren’t symmetrical or when you work in a spiral without controlling the start of the round. Solution: use a stitch marker and distribute changes across 4 “cardinal” stitches.

Frequently asked questions

Can I make it with cord instead of T-shirt yarn?

Yes, but cord usually creates more defined fabric with less “volume.” You can achieve the same structure, although you may need more rounds to reach the same height.

Which stitch is best for the base and sides?

For the base, single crochet is usually the most stable stitch. For the sides, use single crochet or half double crochet (if you want to work faster). If you’re looking for a texture with defined “channels,” try crocheting several rounds through the back loop.

How do I know if my bag will hold weight?

The key is: a compact base + a defined transition + a reinforced top edge + securely attached handles. If you also add a rigid base and lining, you’ll increase its durability.