Free tool
Landscape Fabric Calculator
Fabric is sold by the linear foot off a roll of a fixed width, so the amount you need is not the size of the bed divided by anything. Enter the area and this lays the strips out, allows for the overlap where they meet, and gives you the length to order.
What are you laying it under?
Measure your area
Enter a length and width for this area.
For an irregular area, divide it into rectangles and enter each one separately.
The other half of the job
Working out the rock or mulch that goes on top?
Fabric is measured in linear feet; the material over it is sold by the cubic yard. The material calculator turns an area and a depth into the number of yards to order.
Getting the layout right
- Fabric belongs under decorative rock, which does not break down. Under bark mulch it usually does more harm than good — the mulch is meant to rot into the bed, and fabric stops that reaching the soil.
- Overlap the seams and pin them down. An unpinned edge works its way up through the rock the first time someone rakes it.
- Run the strips whichever way gives the fewest seams. The calculator tries both directions for you and shows the one that costs less.
- For plants already in the bed, cut a slot in from the edge rather than a hole in the middle. A slot can be tucked back down; a hole cannot.
- For an irregular bed, split it into rectangles and enter each one separately. The calculator lays out each area on its own and totals the roll.
The maths behind it
The first strip covers the full width of the roll. Every strip after it gives up part of itself to the overlap, so it only adds the roll width minus the overlap. Divide the width of your bed by that figure, round up, and you have the number of strips.
Each of those strips is cut to the full length of the run, and each one is rounded up on its own to the length we can cut to — never the total, because you cannot buy part of a cut. Strips times cut length is the linear feet. The calculator does that sum both ways round, and for every roll width in stock, then shows you the cheapest of them.
Common questions
How much landscape fabric do I need?
It is not simply the area divided by the roll width. Fabric comes on rolls of a fixed width, neighbouring strips have to overlap along the seam, and every strip is cut to the full length of the run. Enter the length and width of the bed above and this lays the strips out and gives you the linear feet to order.
Do the strips need to overlap?
Yes. Where two strips meet they overlap along the seam so weeds cannot come up between them. The overlap is already included in the quantity above — it is why the answer is a little more fabric than the bare square footage suggests.
Which way should the fabric run?
Whichever direction needs fewer strips, because every seam is a place weeds can find and a place you have to pin. The calculator works out both directions and recommends the cheaper one, and the result tells you which side to run the fabric along.
Do I need landscape fabric under mulch?
Usually not. Bark mulch is supposed to break down into the bed over time, and fabric underneath stops that from happening. Fabric earns its place under decorative rock, gravel, and anything else that does not decompose.
Is fabric sold by the foot or by the roll?
Both, depending on the product. The calculator compares buying loose linear feet against buying a full roll — and a roll plus a loose remainder — and quotes whichever works out cheapest for the amount you need.
How much extra should I order?
The quantity above already covers the overlap at the seams. Adding 10 percent on top is worth it if the bed has curved edges, obstacles to cut around, or if you would rather trim off a bit than come up short. The tick box above adds it.