Why the sheet count is not the area divided by the sheet
Overlap is the whole reason. A flattened box measuring 4 by 2.5 feet is 10 square feet of material, but if it has to overlap its neighbours by six inches on every side, the ground it actually holds down is 3.5 by 2.0 feet, which is 7 square feet. That is a 30 percent difference, and it is why a job estimated at 120 boxes takes 172 of them.
The effect scales badly with small sheets. At a six inch overlap, a 4 by 2.5 ft sheet loses 30 percent; a 2 by 1.5 ft sheet loses 50 percent. If you are collecting boxes for this, the large flat ones are worth several small ones each, and it is worth flattening and measuring a sample before deciding how many you need to save up.
The volume is the part that surprises people
Depth in inches over an area in square feet feels small and is not. The conversion is area times depth in feet, divided by 27:
| Area | 2" deep | 3" deep | 4" deep | 6" deep |
|---|---|---|---|---|
| 500 sq ft | 3.09 cu yd | 4.63 cu yd | 6.17 cu yd | 9.26 cu yd |
| 1,000 sq ft | 6.17 cu yd | 9.26 cu yd | 12.35 cu yd | 18.52 cu yd |
| 2,000 sq ft | 12.35 cu yd | 18.52 cu yd | 24.69 cu yd | 37.04 cu yd |
A two-inch compost layer and a four-inch mulch layer over 1,000 square feet is 6.17 plus 12.35, which is 18.5 cubic yards. In bagged form at 2 cubic feet a bag that is 250 bags. Nobody buys 250 bags twice, which is why the arithmetic is worth doing before the first order rather than after it.
Stripping is a weight problem, not a volume problem
Cutting two inches off 1,000 square feet is 167 cubic feet in the ground, a shade over 6 cubic yards. Loose in a trailer, with bulking, call it 7.7. That part sounds manageable. The weight does not: at around 90 pounds per cubic foot the same material is 15,000 pounds, which is seven and a half tons and well past what a light trailer or a small skip is rated for.
This is the number that decides whether the turf is stripped at all. Covering it in place moves nothing and costs a sheet material plus the layers on top. Stripping it moves several tons off the site and then, quite often, buys soil back to replace what left with it. Neither is wrong, but they are different jobs with different budgets, and the volume figures above are what makes the comparison honest.
The edge is where conversions come undone
A cover of any kind stops at its perimeter, and grass that spreads by runners does not. Whatever holds the boundary — a mowing strip, a deep edge, a hard surface, a band of the cover material carried well past the visible line — is doing more work than anything in the middle of the bed. The area calculation says nothing about it, so treat the perimeter as a separate item with its own materials.
The same applies below ground. Irrigation that used to serve turf is still there under a converted bed, and heads that now sit in the middle of mulch will either be capped, converted, or will spend the next few years watering the mulch. That decision is easier taken before the mulch goes down than after.
Questions people ask
How much overlap should I allow between sheets?
That is a judgement rather than a rule, and the calculator takes whatever you give it. What the arithmetic can tell you is what the choice costs: on a 4 by 2.5 ft sheet, going from a 4 inch overlap to an 8 inch overlap moves the effective coverage from 7.9 sq ft to 6.1 sq ft, which is 30 percent more sheets for the same ground. Small overlaps risk gaps opening as the material settles and wets; large overlaps are material you are paying for twice. Most people land somewhere in the middle and take more care over the perimeter than the field.
Do I need to strip the turf before covering it?
The calculator will price either, and which one applies depends on things it cannot see: what the grass is, how thick the thatch is, whether the finished level has to match a path or a patio, and how much weight you can get off the property. Covering moves nothing and raises the level by the depth of the layers you add. Stripping lowers the level first and generates several tons of spoil. If the finished grade matters, work out both and see which one lands where you need it.
Why does the calculator not tell me how long to leave the cover in place?
Because the honest answer depends on the grass species, the season, the soil and the weather, and any single figure printed here would be wrong for most readers. What is worth knowing is that the timing is set by the plant, not by the material: perennial grasses that spread by rhizome are a different proposition from a bunching annual. Your local extension service publishes that for the species you actually have, which is more use than a number on a web page.
Can I plant straight through the cover?
People do, and the calculator does not have an opinion on it, but there is one consequence worth planning for. Every opening cut in a continuous cover is a place where whatever the cover was suppressing has a route back, so the number of openings and their size is part of the design rather than an afterthought. It also interacts with spacing: a bed planted at wide spacing needs fewer openings but stays open for longer, which is exactly the trade-off the plant spacing and closure calculator puts numbers on.
What do I do about the sprinklers under the lawn I am removing?
Decide before the mulch goes on, because after that you are digging blind for something you can no longer see. The two usual routes are capping the heads on that zone and abandoning it, or converting the zone to drip for the new planting, and the water arithmetic for the second is on the spray to drip conversion calculator. Either way, mark where the laterals run first. A drip line or a low-voltage lighting cable a few inches down offers no resistance to a spade, and the buried loop of a pet fence is in the same category.