A container is billed on two numbers, not one
Roll-off containers are advertised by volume — a 10, 20, 30 or 40 cubic yard box — and priced on a flat hire that includes a stated tonnage. Exceed the tonnage and you pay by the ton on top, at a rate that is frequently the difference between a cheap disposal and an expensive one. So the container you need is whichever is bigger: the one that holds your volume, or the number of hires that carries your weight.
Homeowners size containers by eye, and eyes measure volume. That works while the load is drywall, timber and cabinets, which are bulky and light. It fails badly the moment tile, plaster, mortar or roofing enters the box, because those materials are three to five times heavier per square foot than drywall and take up no more room. A 20-yard box half filled with bathroom tile can be over its tonnage while looking like a wasted hire.
This calculator takes areas rather than volumes because areas are what you can measure off a plan or off the walls. It converts each area to an in-place volume using a typical thickness, expands that by a bulking factor because broken material does not stack the way it sat, and weighs it using typical unit weights. Then it compares the two constraints and prices the overage.
Disposal is a line item in your renovation budget, and it is one of the most commonly excluded items in a contractor's quote — worth checking before you assume it is somebody else's problem.
Bulking, thickness and unit weight
In-place volume is area times thickness. A thousand square feet of half-inch drywall occupies 1,000 × 0.5/12 = 41.7 cubic feet in the wall, which is only 1.54 cubic yards. That figure surprises people, and it is why volume is rarely the binding constraint on interior work.
Bulking is the expansion when the material breaks. Sheet goods torn off a wall arrive in the container as irregular pieces that bridge and void, so the loose volume is larger than the in-place volume — typically 40 to 80 per cent larger for broken board and rubble, less if a crew cuts sheets down and stacks them deliberately, more if long lath and splintered timber are thrown in whole. The calculator applies the factor you enter to the sheet materials only. Cabinets, fixtures and framing are entered directly as loose volume, because you cannot usefully measure their area and you can eyeball the pile they will make.
Unit weight is the term that decides the outcome. The values used here are typical for the materials as they are usually found in housing: half-inch gypsum board at about 1.6 lb per square foot, ceramic tile with its bed of thinset at about 5, three-coat plaster on wood lath at about 8, one layer of asphalt shingles at about 2.5, three-quarter-inch hardwood at about 2.8 (a red oak density of roughly 45 lb/ft³ × 0.0625 ft = 2.8), and carpet with underlay at about 1. Mixed cabinets, fixtures and framing are weighed at 250 lb per loose cubic yard.
Those numbers are representative rather than exact, and two situations shift them materially. A tile floor on a traditional mortar bed can weigh three times the tile alone, so treat a mud-bed floor as if you were removing plaster as well. And any material soaked by weather — carpet after a flood, plaster after a roof leak — gains weight that no dry figure captures.
Worked example: gutting a kitchen and a bathroom
You are stripping 1,200 ft² of drywall from walls and ceilings, 400 ft² of tile, and 600 ft² of wood flooring, plus about 3 yd³ of cabinets, a vanity and old framing. You allow 60% bulking. Your hauler offers a 20 yd³ box including 2 tons, with overage at $75/ton.
- Drywall. Volume 1,200 × 0.5/12 = 50 ft³. Weight 1,200 × 1.6 = 1,920 lb.
- Tile. Volume 400 × 0.5/12 = 16.67 ft³. Weight 400 × 5.0 = 2,000 lb.
- Flooring. Volume 600 × 0.75/12 = 37.5 ft³. Weight 600 × 2.8 = 1,680 lb.
- Bulk the sheet goods. 50 + 16.67 + 37.5 = 104.17 ft³; × 1.60 = 166.67 ft³; ÷ 27 = 6.17 yd³.
- Add the loose items. 6.17 + 3.00 = 9.17 yd³ total volume.
- Total weight. 1,920 + 2,000 + 1,680 = 5,600 lb, plus 3 yd³ × 250 = 750 lb, giving 6,350 lb ÷ 2,000 = 3.18 tons.
- Containers on volume. ceil(9.17 ÷ 20) = 1.
- Containers on weight. ceil(3.18 ÷ 2) = 2.
- Overage if you hire one box. 3.18 − 2.00 = 1.18 tons × $75 = $88.13.
One 20-yard box holds this load comfortably — it is less than half full — and still costs you $88 of overage. That is the entire point of the calculation. Note also which material did the damage: the tile is 400 ft² against the drywall's 1,200 ft², yet it contributes more weight (2,000 lb against 1,920 lb) and less than a third of the volume.
How to act on the two container counts
Order the larger of the two counts. If weight binds, a second hire is often cheaper than the overage on the first, and it is always cheaper than the alternative outcome — an overloaded box the hauler refuses to lift, which some operators charge a dry-run fee for and all of them charge time for.
Where weight binds because of one heavy material, separate it. The standard trade practice is a small dedicated container for rubble — tile, plaster, mortar, concrete — and a larger one for everything else. Haulers frequently price a clean-rubble box below a mixed-waste box, because clean inert material goes to a different, cheaper facility. Ask; the difference is worth a phone call.
Watch the fill line, not just the total. Containers must be loaded level with the top rail to be legal on the road. If your calculated volume needs a box filled to the brim, size up. The practical capacity of a roll-off is usually reckoned at around 80 to 90 per cent of its nominal volume once loading is honest.
Check the tonnage on your quote, not the one you remember. Included allowances vary from about one ton on a 10-yard box to four or more on a 40. Two haulers quoting the same hire price with a one-ton difference in the allowance are not quoting the same thing — the arithmetic here is the same levelling exercise the quote comparison calculator does on a whole project.
Typical unit weights and thicknesses used here
| Material | Assumed thickness | Unit weight (lb/ft²) | Weight per 100 ft² (lb) |
|---|---|---|---|
| Drywall, 1/2 in | 0.5 in | 1.6 | 160 |
| Ceramic tile with thinset | 0.5 in | 5.0 | 500 |
| Plaster on wood lath | 1.0 in | 8.0 | 800 |
| Asphalt shingles, one layer | 0.25 in | 2.5 | 250 |
| Wood flooring, 3/4 in | 0.75 in | 2.8 | 280 |
| Carpet and underlay | 0.5 in | 1.0 | 100 |
| Cabinets, fixtures, framing | entered as loose volume | 250 lb per yd³ | — |
Representative values for common residential construction. A mortar-bed tile floor, a slate or tile roof, or any material saturated with water will exceed these substantially; where yours does, scale the area you enter to match the weight you expect.
Things that add weight or cost after the estimate
- A second layer of shingles. Re-roofing over an existing layer is common; stripping both doubles the tonnage from that item alone.
- Mortar beds under tile. A traditional bed adds far more weight than the tile above it, and is only visible once the first tile lifts.
- Water. Rain into an open container over a weekend is charged to you by the ton. Ask for a tarp or a lidded box in wet weather.
- Prohibited items. Paint, solvents, batteries, tyres, appliances containing refrigerant, and pressure-treated lumber are excluded from mixed loads by most haulers and attract a separate charge if found.
- Asbestos and lead. In housing built before about 1980, floor tile, mastic, pipe lagging and textured coatings may contain asbestos, and paint may contain lead. Both are regulated waste streams with their own disposal routes, and neither belongs in a general container. Test before you demolish.
- Permits for the container itself. A box standing on a public street needs a permit in many municipalities, and the fine for one without is not small.
- Extra rental days. Hires include a fixed number of days; a project that slips carries daily charges. Estimate the programme with the project duration calculator before you book the drop.
Reducing what you throw away
The cheapest ton is the one that never enters the box, and demolition offers more scope for that than most people expect.
Separate clean streams where the volume justifies it. Clean timber, clean gypsum, metal and clean rubble all have separate outlets. Scrap metal — old radiators, cast-iron waste pipe, copper, appliances — usually has positive value and always has weight; removing it from the box directly reduces your tonnage. Clean drywall is accepted for recycling in some regions, which matters because it is the highest-volume item in most interior demolitions.
Deconstruct rather than demolish where the fittings are worth something. Cabinets, doors, solid timber flooring, sanitaryware in good order and light fittings are often taken by architectural salvage or reuse charities, sometimes with collection included. This removes bulky, awkward volume from the container and can carry a tax benefit for a donated item in some jurisdictions.
Plan the sequence so the heavy material goes in first. Rubble at the bottom, bulky light material on top, everything broken down rather than thrown in whole. A container packed by someone who cares routinely holds a third more than one filled casually, which can be the difference between one hire and two.
Once you know the disposal cost, it feeds two other decisions: whether to take the demolition on yourself, which the DIY versus contractor calculator settles once your hours are priced, and how large a buffer the project needs, since hidden conditions revealed during tear-out are the classic contingency draw — size that with the contingency calculator.