The job
Modelled, not recorded. Every figure on this page is re-run through the calculator it names whenever the site is built; the estimate is worked, but no job was carried out, so the last section gives the mechanism of each likely error rather than a measured overrun.
A replacement driveway is two jobs sold as one. The first is getting 600 sq ft (55.7 m²) of old concrete off the property, which is booked by weight rather than by the yard; the second is a new slab on a subgrade nobody has seen until the first job is finished. The quantities below follow the work in its own order, because the break-out decides the haul, the haul uncovers the subgrade, and the subgrade decides how much base and concrete everything after it needs.
The job: a single-car driveway 12 ft wide and 50 ft long (3.66 × 15.24 m), running from the garage slab to the public sidewalk. The old slab comes out, the ground beneath is taken down to a new subgrade, and a new 4 in (102 mm) slab goes back on 4 in (102 mm) of compacted gravel, reinforced with #3 bar at 18 in (457 mm) each way and given a broom finish. Both ends meet concrete that stays — the garage slab at one end, the sidewalk at the other — so the finished surface is fixed at both ends before a single figure is taken.
START WITH HOW THICK THE OLD SLAB REALLY IS. It sets the weight leaving site, and because the new surface is pinned at both ends, it sets where the old base sits against the new subgrade. A 4 in slab on a 4 in base needs its subgrade 8 in (203 mm) below the finished surface; under a 4 in old slab, the old base already fills the layer the new base needs. So the old base is either reworked in place or dug out and replaced. This model takes the second, heavier case and says below where that choice moves the numbers.
AND CONCRETE LEAVES BY WEIGHT BUT ARRIVES BY VOLUME. A dumpster loaded with broken slab is over its weight allowance well before it looks full, so the haul is planned in tons; the new concrete is ordered in cubic yards and cannot be topped up once the first truck has started to stiffen. Those are the two lines where an error is expensive in one direction only: a short haul booking costs another trip, a short concrete order costs a cold joint across the driveway.
WHAT IS NOT HERE. The site's tool list carries no breaker or jackhammer, so the equipment that does the first day's work is not linked below. The driveway calculator applies one depth across the whole slab, so a thickened edge, or a thickened end where the drive meets the sidewalk, is extra concrete this page does not count. No driveway was broken out for this page; each quantity is what the linked calculator returns for the stated dimensions.
What was measured, and how
Driveway plan, garage slab to sidewalk edge
50 × 12 ft (15.24 × 3.66 m): 600 sq ft (55.7 m²)
Taken along both edges and across at both ends and the middle, because an old driveway is seldom square to the garage and a single width hides a taper. The common error is measuring on to the street curb, which folds in the apron beyond the sidewalk — often built to the city's own detail under its own permit and taken off separately.
Old slab thickness, found at the broken edge
4 in (102 mm) taken throughout for this model: 200 ft³, or 7.41 yd³ (5.66 m³) in place
Read with a tape at the first saw cut, at several points down both sides and at each end, rather than assumed from the nominal figure. Old driveways were often poured thick over low ground or at the street end, and taking 4 in everywhere under-books the haul and puts the new subgrade in the wrong place.
Finished levels at the two fixed ends
New surface flush with the garage slab and the sidewalk, falling away from the garage
Both ends are levelled from the concrete that stays: a laser reading on the garage slab edge and another on the sidewalk edge, taken while the old drive is still whole and carried out to offset stakes with a string between them. The old surface is no reference — it leaves in the first haul, and anything read from the ground after that has already moved.
Subgrade depth and base width
Subgrade 8 in (203 mm) below finished level; 4 in (102 mm) of new base, 13 ft (3.96 m) wide: 650 sq ft (60.4 m²)
Measured down from the string lines, never from the top of the old base, which the break-out ruts and loosens. The width is the slab plus a shoulder each side so the form stakes and the slab edge bear on compacted stone; leaving the shoulders out puts both on the bare subgrade.
The takeoff, in order
Each step needs something from the one before it, which is why the order is part of the answer.
Size the break-out as loose volume
- Needs
- The in-place volume from the plan and the thickness found at the broken edge — 50 × 12 ft at 4 in is 200 ft³, or 7.41 yd³ (5.66 m³) — with concrete chosen as the material.
- Produces
- The volume the slab occupies once broken, larger than the slab because the pieces stack with voids between them, and the figure a container is sized against. The calculator bulks concrete by a factor of 1.3, where the linked demolition guide puts broken concrete nearer one and a half times its solid volume, so a container sized on this figure has little room to spare. The weight the next step makes of it is the steadier number, because the concrete weighs the same however loosely it stacks.
Result9.63 yd³ (7.36 m³) of loose rubble
Demolition Bulk Volume Swell CalculatorTurn the rubble into a weight for the haul
- Needs
- The loose 9.63 yd³ from step one. The converter's density is for broken concrete with its voids, so entering the slab's solid 7.41 yd³ instead would understate the weight by close to a quarter.
- Produces
- The weight that books the dumpster or the trucks, and the number a hauler's weight allowance is checked against. It covers the slab alone; the old base dug out beneath it leaves as a second load, weighed with the new stone in step three.
Result14.4 short tons (13.1 t) of broken concrete
Concrete Rubble Cubic Yards to Tons CalculatorQuantify the new gravel base
- Needs
- The subgrade left once the rubble from step two and the old base are gone, the 4 in (102 mm) compacted depth the fixed levels allow, and the 650 sq ft (60.4 m²) base area with its shoulders. Run first over the old slab's 600 sq ft (55.7 m²) at the same 4 in, this calculator weighs the old base as that second haul: 13.7 short tons (12.5 t) of stone in place, before any soil that comes up bonded to it.
- Produces
- The compacted tonnage at 137 pcf (2,200 kg/m³), which is the calculator's default for a compacted dense-graded base — about the 1.85 short tons per cubic yard a highway department pays on; the supplier's own compacted density replaces it on the order. Stone is bought by the ton here since it arrives loose and only reaches this thickness once compacted in lifts with the plate compactor. Its volume line, 8.02 yd³ (6.14 m³), is larger than the base line the driveway calculator prints in step eight, because that one leaves out the shoulders.
Result14.9 short tons (13.5 t) at 137 pcf (2,200 kg/m³) compacted
Gravel Base Layer Tonnage CalculatorQuantify the isolation joints at the two fixed ends
- Needs
- The compacted base from step three for the filler to stand on, and the 24 ft (7.3 m) of ends from the plan — 12 ft (3.66 m) against the garage slab and 12 ft against the sidewalk — with ½ in (13 mm) fibre filler set to the slab depth less a ¼ in (6 mm) sealant reservoir.
- Produces
- The sealant for that reservoir at two to one, width to depth. The volume is small, so whole cartridges govern it; the filler strip is bought by length, 24 ft (7.3 m) of it, and set against the old concrete before any form goes up, since the concrete that stays fixes where both ends fall.
Result0.16 gal (20 US fl oz, 0.59 L) of sealant, a little under two 10.1 fl oz (300 mL) cartridges
Concrete Expansion Joint Filler CalculatorSet the edge forms on the compacted base
- Needs
- The compacted base from step three, which the stakes are driven into, the isolation strips from step four that close both ends, and the slab's 50 × 12 ft (15.24 × 3.66 m) plan with its 4 in (102 mm) edge.
- Produces
- The board count with the calculator's cutting allowance set to nothing. It forms all four sides; this driveway is formed on the two long ones, and the 24 ft (7.3 m) of ends it counts, already closed by the step-four strips, is more than its default allowance would add to the sides. A 2x4 dresses to 3½ in (89 mm), ½ in (13 mm) shy of this edge, so a 2x4 set to the string stands ½ in clear of the base: either the gap under it is packed or banked outside, or 2x6 stock is set down into the shoulder.
Result16 boards of 8 ft (16 of 2.4 m on the metric setting)
Concrete Formwork CalculatorLay out the steel grid inside the forms
- Needs
- The formed rectangle from step five and the isolation joints from step four — the bars stop short of the filler rather than tying into the garage slab or the sidewalk — with #3 bar chosen at 18 in (457 mm) each way.
- Produces
- Nine bars along the length and 34 across: 987 ft (301 m) of bar including the calculator's default lap allowance. The grid runs edge to edge, so cover at the forms is not deducted, and each 50 ft (15.24 m) run takes two laps at the 20 ft stick length.
Result50 sticks of 20 ft (26 of 12 m on the metric setting)
Rebar CalculatorCount the chairs that hold the grid up
- Needs
- The grid from step six — nine bars across the 12 ft (3.66 m) width at 18 in (457 mm) — and a support spacing of 3 ft (0.91 m) along each bar, chosen for a mat that will be walked on and confirmed against the chair maker's data, with every bar carried.
- Produces
- Seventeen support lines each carrying all nine long bars, with the cross bars resting on them. The calculator's own help says a light mat cannot span between supported bars and sags between the ones that are held, and #3 at 18 in is a light mat; carrying every second bar would cut the count to 85, a saving only a stiffer grid earns. The chairs stand on the gravel from step three, so they are the kind with a base or plate that bears on stone rather than punching into it; chair height follows from the cover and is not calculated here.
Result153 chairs (or 204 ft / 62.2 m of continuous bolster)
Rebar Chair and Bolster Count CalculatorOrder the concrete
- Needs
- The depth the forms from step five leave above the base from step three — checked with a tape from the string line down to the top of the compacted base before ordering, not read off the drawing — and the 50 × 12 ft (15.24 × 3.66 m) plan that the forms and the step-four strips enclose.
- Produces
- The neat volume at one depth throughout, with nothing added. It takes a small allowance and is then rounded up to the plant's ordering increment; a thickened edge, or a thickened end where the drive meets the sidewalk, is extra and outside this figure. Its base line of 7.41 yd³ covers the slab rectangle only, which is why the stone was ordered from step three instead.
Result7.41 yd³ (5.66 m³) of concrete, neat
Concrete Driveway CalculatorLay out the control joints
- Needs
- The 4 in (102 mm) depth confirmed before the order in step eight, the isolation joints at each end from step four, and the 12 ft (3.66 m) width from the forms in step five, because the width alone decides whether a joint runs down the middle.
- Produces
- The spacing ceiling. The 12 ft width exceeds it, so a joint runs down the centre line, making 6 ft (1.83 m) panels; keeping each no longer than about one and a half times its width puts the cross joints at 8 ft 4 in (2.54 m) — six panels a side, five cross cuts and 110 ft (33.5 m) of saw cut, taken to a quarter of the slab depth, 1 in (25 mm).
Result10 ft (3.05 m) maximum joint spacing
Concrete Control Joint Spacing CalculatorQuantify the curing compound
- Needs
- The finished area from step eight, 600 sq ft (55.7 m²), the broom finish it receives, and the product's data-sheet coverage of 200 sq ft to the US gallon (4.9 m²/L).
- Produces
- One coat as run, sprayed once the bleed water has gone from the surface. On a broom finish the linked curing guide treats two coats at right angles as standard, which doubles the order to 6.0 US gal (22.7 L) at the same rate. The calculator also notes that a textured surface takes more compound than a trowelled one at the same rated coverage, so the compound is bought in whole containers above the two-coat figure.
Result3.0 US gal (11.4 L) for one coat
Concrete Curing Compound Coverage Calculator
The figures
| Step | Calculator | Figure |
|---|---|---|
| Size the break-out as loose volume | Demolition Bulk Volume Swell Calculator | 9.63 yd³ (7.36 m³) of loose rubble |
| Turn the rubble into a weight for the haul | Concrete Rubble Cubic Yards to Tons Calculator | 14.4 short tons (13.1 t) of broken concrete |
| Quantify the new gravel base | Gravel Base Layer Tonnage Calculator | 14.9 short tons (13.5 t) at 137 pcf (2,200 kg/m³) compacted |
| Quantify the isolation joints at the two fixed ends | Concrete Expansion Joint Filler Calculator | 0.16 gal (20 US fl oz, 0.59 L) of sealant, a little under two 10.1 fl oz (300 mL) cartridges |
| Set the edge forms on the compacted base | Concrete Formwork Calculator | 16 boards of 8 ft (16 of 2.4 m on the metric setting) |
| Lay out the steel grid inside the forms | Rebar Calculator | 50 sticks of 20 ft (26 of 12 m on the metric setting) |
| Count the chairs that hold the grid up | Rebar Chair and Bolster Count Calculator | 153 chairs (or 204 ft / 62.2 m of continuous bolster) |
| Order the concrete | Concrete Driveway Calculator | 7.41 yd³ (5.66 m³) of concrete, neat |
| Lay out the control joints | Concrete Control Joint Spacing Calculator | 10 ft (3.05 m) maximum joint spacing |
| Quantify the curing compound | Concrete Curing Compound Coverage Calculator | 3.0 US gal (11.4 L) for one coat |
The waste factors, and why these ends of the ranges
| Material | Applied | Why |
|---|---|---|
| Ready-mix concrete | The neat volume plus a small margin, taken to the next ordering increment the plant accepts | The 7.41 yd³ is geometry on a base assumed flat, and a base laid over a dug-out subgrade seldom is. Low spots in the top of the base become extra slab depth, and form boards that bow outward add width along a 50 ft (15.24 m) run. The asymmetry sets the end of the range: excess is a fraction of a yard returned to the plant, while a shortfall is a second truck, a wait and a cold joint across the driveway. |
| Gravel base | The upper end of the usual margin, because the subgrade follows a break-out rather than a clean cut | The calculator applies no margin, and the 5 to 10% its FAQ suggests for spillage and minor over-excavation assumes a tidy excavation. Breaking out an old drive is not one: the old base leaves in uneven lumps, soft ground shows when the compactor passes over it, and the stone that levels each hollow is volume the plan area never contained. |
| Rebar | Counted from a cut list against the stick length rather than from total length | The stick count divides total length by 20 ft and assumes every offcut is used. Each 12 ft cross bar cut from a 20 ft stick leaves an 8 ft (2.44 m) end that only counts if it is lapped into a long run, while the default 15% lap allowance is generous for #3 bar. A cut list settles which effect wins on this grid. |
| Form boards | The calculator's full perimeter with its own cutting allowance set to nothing | The calculator forms all four sides and this driveway is formed on two, its ends closed by the isolation strips against the old concrete. The 24 ft (7.3 m) of ends it counts but the job leaves unformed is more than its default 10% would add to the two long sides, so taking the allowance as well would buy the laps twice. Stakes sit outside the count either way and are bought separately. |
| Joint sealant and curing compound | Whole cartridges and whole containers above the computed volume, with the curing rate from the product's own data sheet and a second coat on the broom finish | Both are small volumes where the package dominates. The sealant reservoir takes most of two cartridges before any tooling loss. The curing compound is ordered for two coats at right angles, which the linked curing guide treats as standard on textured work and which doubles the one-coat figure, and a broomed surface still meets more area than its 600 sq ft (55.7 m²) plan, as the calculator notes. |
Where this estimate is most likely to be wrong
Rubble weight and the number of loads
usually underSeveral things push the real haul above the computed one, and only a slab thinner than nominal pulls it below. Old driveways are often thicker than nominal at the street end and over old low spots; base stone and soil come up bonded to the underside; and wire mesh or bar in the old slab holds broken pieces together, so they stack loosely and fill a container by volume sooner than the swell factor predicts.
Narrow it by: Cutting and lifting a small square near the garage, another mid-drive and a third by the sidewalk to read the true thickness, and checking the broken edges for mesh or bar, before any container is booked.
Gravel base tonnage
either wayThe tonnage assumes a new 4 in layer on a clean subgrade. If the old base comes out of the break-out clean and sound, it can be regraded, recompacted and only topped up, which pulls the order well below this figure; if the break-out ruts it, mixes soil into it or exposes soft ground, stone fills every low spot and pushes the order above it.
Narrow it by: Proof-rolling the exposed old base with a loaded truck or barrow wheel before deciding, and ordering stone after the break-out rather than with it.
Concrete
usually underThe figure is one uniform depth on a flat base. Every low spot in the top of the compacted base is extra slab depth, and each extra half inch (13 mm) across this driveway is close to another cubic yard — 0.93 yd³ (0.71 m³); form boards that bow under the pour add width along the 50 ft sides. A thickened edge, or a thickened end where the drive meets the sidewalk, is outside the calculation altogether.
Narrow it by: Checking depth from string line to compacted base on a grid the day before the pour, and taking off any thickened edge or end as its own strip.
Rebar sticks
either wayTwo simplifications pull against each other. The flat lap allowance is generous for #3 bar, whose laps at 40 to 48 bar diameters are well under 2 ft (0.61 m), but the stick count assumes every offcut is reused — and each 12 ft cross bar cut from a 20 ft stick leaves an 8 ft (2.44 m) end that only counts if it is lapped into a long run.
Narrow it by: Writing a cut list for the nine long bars and the 34 cross bars against the stick length before ordering, instead of dividing total length by 20 ft.
Break-out time and equipment
usually underThis page quantifies what leaves site, not the effort of getting it out. Mesh or bar in the old slab has to be cut free before the pieces can be loaded, a thicker slab breaks more slowly, and the site's tool list has no breaker, so the equipment that governs the first day is chosen outside this takeoff entirely.
Narrow it by: Breaking a test section at the first saw cut to see the thickness and the steel before choosing the equipment and booking the haul.
Tools this job needs
Frequently asked questions
- How much concrete do I need for a 12 × 50 driveway?
- At 4 in (102 mm) thick, a 12 × 50 ft (3.66 × 15.24 m) driveway takes 7.41 yd³ (5.66 m³) of concrete, neat. That assumes one depth on a flat base. Add a small allowance and round up to the plant's ordering increment, because low spots in the base become extra slab depth — each half inch (13 mm) across this driveway is close to another cubic yard, 0.93 yd³ (0.71 m³). A thickened edge or a thickened end at the sidewalk is counted separately.
- How thick should a concrete driveway be?
- 4 in (102 mm) is the common thickness for a driveway carrying cars, laid here on 4 in (102 mm) of compacted gravel; the driveway calculator points to 5–6 in (127–152 mm) where heavier vehicles use it regularly. Thickness also sets the joints: at 4 in the maximum control-joint spacing is 10 ft (3.05 m), so a 12 ft (3.66 m) wide drive needs a joint down its centre.
- How many tons of concrete come out of a 12 × 50 driveway?
- At 4 in (102 mm) thick the slab is 7.41 yd³ (5.66 m³) in place, which breaks out to 9.63 yd³ (7.36 m³) of loose rubble weighing 14.4 short tons (13.1 t). Digging out the old 4 in base is a second haul, 13.7 short tons (12.5 t) of stone. The new work takes 14.9 short tons (13.5 t) of gravel, 16 form boards, 50 sticks of 20 ft rebar (26 of 12 m) on 153 chairs, and 7.41 yd³ (5.66 m³) of concrete.