Quilt Backing CalculatorQuilt Size Calculator
A quilt's job is to cover a mattress and hang gracefully over its edges — so the right size starts at the bed, not at a chart of conventions. Pick your mattress, choose how far down the sides you want the quilt to fall (the "drop"), and this calculator works out the dimensions to make.
Quilt Size Calculator
Recommended width = mattress width + drop on both sides; recommended length = mattress length + drop at the foot (the top edge usually stops at the pillows). Once you have dimensions, the natural next steps are the backing calculator for the fabric behind it and the batting calculator for the layer inside it.
How it's calculated
The arithmetic is household geometry: width = mattress W + 2 × drop, length = mattress L + drop. Mattress sizes are the US standards shown in the chart below. Standard quilt sizes are the commonly published finished dimensions — they vary a little between designers, which is exactly why this calculator works from your mattress and your drop first, and only then names the nearest standard size as a shopping convenience.
How much drop do you actually want?
Drop is the difference between a quilt that looks tailored and one that looks borrowed. On a typical bed — mattress about 12 in deep on a frame — a 10 in drop leaves the quilt ending just below the mattress edge, a comforter look that suits modern low beds. Fifteen inches covers the mattress and half the box spring or bed base: the most versatile, most chosen look. Around 20 in, the quilt becomes a coverlet, hiding the base almost entirely; 25 in and more approaches a traditional bedspread that pools toward the floor.
Length has its own convention: no drop is added at the head, because pillows occupy that space — but if you like the quilt folded back over the pillows, or tucked over them bedspread-style, add 10–15 in to the recommended length manually and treat the width figure as the one that matters.
After the size: backing and batting
A recommended size is a starting gun, not a finish line. If you are piecing the top from blocks, take these dimensions to the block calculator and let the grid round them to something buildable. Whatever final size you settle on, the same two dimensions drive the layers: backing is cut to the top plus overage, and batting is bought to the same footprint. Both have calculators on this site, linked from the result above — size them from the finished top, measured, not from the plan.
How to use this calculator
- Recommended width = mattress width + 2 × drop (one drop for each side).
- Recommended length = mattress length + drop (foot end only — the top tucks at the pillows).
- Compare against the standard quilt sizes and name the smallest standard size that covers both recommendations.
Standard quilt and mattress sizes
Standard finished quilt sizes
| Quilt size | Finished dimensions |
|---|---|
| Crib | 36 × 52 in |
| Throw | 50 × 65 in |
| Twin | 70 × 90 in |
| Full / Double | 80 × 90 in |
| Queen | 90 × 108 in |
| King | 110 × 108 in |
Mattress top sizes
| Mattress | Top dimensions |
|---|---|
| Crib | 28 × 52 in |
| Twin | 39 × 75 in |
| Twin XL | 39 × 80 in |
| Full / Double | 54 × 75 in |
| Queen | 60 × 80 in |
| King | 76 × 80 in |
| California King | 72 × 84 in |
Finished quilt sizes are the most commonly published chart values; individual pattern designers vary by a few inches. Mattress sizes are US standards.
Related calculators
- Quilt Batting CalculatorQuilt batting calculator: enter your quilt size to get the batting dimensions needed and the smallest pre-cut package that fits, or yardage from a 90 in bolt.
- Quilt Backing Yardage ChartQuilt backing yardage chart: backing size, panel count and yardage for every standard quilt size on 44 in and 108 in fabric, with the method fully explained.
- Quilt Block CalculatorQuilt block calculator: from block size and target quilt size, get blocks across, blocks down, total block count and the exact finished dimensions of the grid.
Got your dimensions? The site's main backing calculator converts them into panels and yardage.
Frequently asked questions
Why is a queen quilt 90 × 108 when the mattress is only 60 × 80?
Because of the drop: 60 + 15 in each side = 90 in wide, and 80 + drop at the foot plus extra length for the classic generous hang gives the length. Standard quilt sizes bake in a healthy drop and a pillow allowance, which is why they look so much bigger than the mattress on paper — on the bed, they are exactly right.
What size is a throw quilt? It has no mattress.
Throws are sized for laps and sofas, not beds: 50 × 65 in is the common standard, generous enough to tuck around feet on a couch. This calculator's chart includes the throw among the standard quilt sizes even though it has no matching mattress.
Twin XL beds in dorms — what quilt fits?
A twin XL mattress is 39 × 80 in, 5 in longer than a standard twin. With a 15 in drop the recommendation is 69 × 95 in — longer than a standard twin quilt (70 × 90). Dorm quilters: make the twin quilt and accept a shorter foot hang, or add a border row to reach the length; the standard width is fine.
Should a quilt be bigger for a taller mattress?
Only if you want the same look. The drop is measured from the mattress top edge, so a deeper mattress doesn't change the geometry of the hang — the quilt ends at the same height above the floor regardless. What a deeper mattress does change is how much of it the drop covers: 15 in of drop on an 18 in mattress barely reaches the base. Judge drop against the finished bed, not the mattress alone.
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