Garbage Bag Size Calculator

Adjust the calculator values below

Purchase size (rounded up) 20 × 31 in
Minimum flat bag width 20 in
Minimum bag length 31 in
Bin opening perimeter 40 in
Bottom allowance 5 in
Overhang or tie allowance 4 in
Rounding increment 1 in
Shape formula Width = bin length + bin width
20 × 31 in
Purchase size (flat width × bag length) 8 × 12 × 22 in rectangular bin, 4 in overhang, rounded upward to whole inches
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Garbage Bag Size Calculator

Use this garbage bag size with trash can shape, bin width, and bin length to get fast results, understand the formula behind the calculation, and...

Use the formula for the bin opening shape

For a rectangular bin, flat bag width equals bin length plus bin width; a square is the same formula with equal sides. For a round bin, flat bag width equals diameter multiplied by π and divided by 2. These widths are half the opening perimeter because a flat bag has two layers.

Add bin height, bottom coverage, and overhang

Bag length equals bin height plus the overhang or tie allowance plus enough material to cross half the bin opening. For rectangles and squares, the bottom allowance is one quarter of the flat bag width. For circles, it is half the diameter. Purchase rounding is applied only after the minimum dimensions are calculated.

Check the bag construction and real fit before buying

The estimate assumes a conventional flat bag and simple bin geometry. Rim thickness, taper, handles, liners, lids, side gussets, star seals, drawstrings, elastic tops, unusually bulky contents, and manufacturer dimension conventions can change the fit. Choose a marketed size at least as large as both rounded dimensions and test the bag on the actual bin when fit matters.

Frequently asked questions

Common questions about rectangular, square, and round-bin formulas, flat bag width, bag length, bottom allowance, purchase rounding, mixed units, and fit limitations.

How is flat bag width calculated for a rectangular bin?

Add the bin length and width. That sum is half the opening perimeter, matching the two layers of a conventional flat bag. For a square bin, the result is twice one side.

How is flat bag width calculated for a round bin?

Multiply the bin diameter by π and divide by 2. This is half the circular opening circumference.

How is the required bag length calculated?

Add bin height, the entered overhang or tie allowance, and the bottom allowance. Bottom allowance is one quarter of flat bag width for rectangular and square bins, or half the diameter for a round bin.

What does purchase rounding do?

It rounds both calculated minimum dimensions upward to the entered increment. It never rounds a dimension below the minimum, so a 34.56-inch width rounded to whole inches becomes 35 inches.

Can I mix measurement units?

Yes. Each bin dimension and the rounding increment can use a different supported unit. The calculator converts them internally and displays all results in the selected result unit.

Why might a bag with these dimensions still not fit?

Gussets, star seals, drawstrings, elastic tops, rim thickness, taper, handles, lids, bulky contents, and manufacturer dimension conventions can change usable fit. Check the product's stated flat dimensions and test the actual bin when needed.