Contractor Estimating Kit · Chapter 1
Measure quantities before you price anything
Most bad estimates don’t go wrong on price. They go wrong on quantity. If you figure 10 yards of concrete and the pour takes 12, no unit price will save the job. So this kit starts here: first you measure how much material the work takes, and only then do you price it.
That list is your takeoff, and it has zero dollar signs on it.
Why keep quantity and price apart
- You can check your work. A number that looks off is easy to spot before it gets buried under markup and tax.
- You can bid it out. Send every supplier the same list and compare price to price, not guess to guess.
- You learn from every job. When the job closes, compare what you measured to what you actually bought. The gap is your real waste factor, and your next estimate gets better.
The rule for this chapter: if a price shows up on your quantity sheet, you’re not done measuring.
Units by trade
Every material is bought in its own unit. Measuring in the wrong one is the most common beginner mistake.
| Trade / material | Measure in | Order in |
|---|---|---|
| Concrete (slabs, beams, footings) | cubic feet | cubic yards |
| CMU, brick | wall square feet | pieces |
| Rebar | linear feet | 20 ft sticks |
| Framing studs | wall linear feet | pieces |
| Plates | linear feet | stock lengths |
| Drywall | square feet | sheets (4×8 = 32 sq ft, 4×12 = 48 sq ft) |
| Roofing (shingles) | roof square feet | squares (1 square = 100 sq ft), bundles per the wrapper |
| Paint | paintable sq ft × number of coats | gallons or 5-gal buckets, per the label’s coverage |
| Flooring and tile | square feet | boxes (sq ft per box is printed on the box) |
| Base, trim | linear feet | stock lengths |
| Plumbing, electrical | fixtures, outlets, runs | pieces and fittings |
Conversions you’ll use every week:
- 1 cubic yard = 27 cubic feet
- 4 inches = 0.333 ft; 6 inches = 0.5 ft
- 80-lb bag of concrete ≈ 0.60 cu ft, so 45 bags per cubic yard
- 60-lb bag ≈ 0.45 cu ft, so 60 bags per cubic yard
EXAMPLE 1: a 20 × 30 ft slab
Take a 20 × 30 ft slab, 4 inches thick, with a perimeter beam 12 inches wide that drops 12 inches below the bottom of the slab. All dimensions are EXAMPLE numbers. On a real job they come from the plans or the tape, never from eyeballing a photo.
Step 1. Slab area
20 ft × 30 ft = 600 sq ft
Step 2. Slab volume
600 sq ft × 0.333 ft = 200 cu ft 200 ÷ 27 = 7.41 CY
Step 3. Beam volume
Measure the beam on its centerline, not the outside perimeter. The outside perimeter counts all four corners twice.
- Outside perimeter: 2 × (20 + 30) = 100 LF
- Centerline (beam is 1 ft wide, so each dimension loses 1 ft): 2 × (19 + 29) = 96 LF
- Extra beam section below the slab: 1 ft × 1 ft = 1 sq ft
- Volume: 96 LF × 1 sq ft = 96 cu ft ÷ 27 = 3.56 CY
Step 4. Total and waste
200 + 96 = 296 cu ft = 10.96 CY
At 5% waste: 10.96 × 1.05 = 11.51 CY. Most plants sell in half-yard increments, so round up: order 12 CY.
For scale: 12 CY in 80-lb bags would be 12 × 45 = 540 bags. That’s why a slab this size comes off a truck.
Step 5. Slab rebar
EXAMPLE: #4 bars at 18 inches on center each way, 3 inches of edge cover.
- Bars running the 30 ft direction: usable width is 20 ft minus 6 in = 234 in. 234 ÷ 18 = 13 spaces, so 14 bars at 29.5 ft = 413 LF
- Bars running the 20 ft direction: usable length is 30 ft minus 6 in = 354 in. 354 ÷ 18 = 19.67, round up to 20 spaces, so 21 bars at 19.5 ft = 409.5 LF
- Total: 822.5 LF
With 15% for laps and waste: 822.5 × 1.15 = 945.9 LF ÷ 20 = 47.3, so order 48 sticks. The 29.5 ft runs need a splice because stock is 20 ft. If your engineer calls for long laps, count them as their own line instead of hiding them in the percentage.
EXAMPLE 2: a CMU wall
A wall 40 ft long and 8 ft high with one 4 × 4 ft window. Standard 8 × 8 × 16 block (nominal size, joint included).
Step 1. Block per square foot
Each block covers 16 in × 8 in = 128 sq in = 0.889 sq ft. So 1 ÷ 0.889 = 1.125 block per sq ft.
Step 2. Net area
40 × 8 = 320 sq ft. Minus the window (16 sq ft) = 304 sq ft.
Step 3. Pieces
304 × 1.125 = 342 block. At 5% waste: 342 × 1.05 = 359.1, order 360.
Step 4. Vertical rebar
EXAMPLE: one bar every 48 inches. 40 ft = 480 in ÷ 48 = 10 spaces + 1 = 11 bars at 8 ft = 88 LF.
Count this one by cut pattern. One 20 ft stick gives you two 8 ft pieces and a 4 ft drop. Eleven pieces ÷ 2 = 5.5, so order 6 sticks. Dividing 88 LF by 20 gives 4.4, and you’d come up short on site.
Waste factors: ranges, not rules
These ranges are common in the trade. Use them as a starting point and adjust them to your own history. Your crew, your suppliers, and the type of work all move the number.
| Material | Typical range |
|---|---|
| Ready-mix concrete | 5-10% |
| CMU and brick | 5-10% |
| Rebar (with laps) | 10-15% |
| Framing lumber | 10-15% |
| Drywall | 10-15% |
| Shingles | 10-15% (more on cut-up roofs with lots of hips and valleys) |
| Tile, straight lay | 10% |
| Tile, diagonal | 15-20% |
| Paint | 10% |
When a job closes, write down what you really bought. If you measured 342 block and used 370, your real waste was 8%, not 5%. That number is worth more than any chart.
Filled takeoff sheet (EXAMPLE)
| Item | Unit | Measured qty | Waste % | Qty with waste | Order | Note |
|---|---|---|---|---|---|---|
| EXAMPLE · Slab concrete, 4 in | CY | 7.41 | 5 | 7.78 | one pour with the beam | |
| EXAMPLE · Perimeter beam 12×12 in | CY | 3.56 | 5 | 3.74 | 12 CY total | measured on centerline |
| EXAMPLE · #4 slab rebar @ 18 in | LF | 822.5 | 15 | 945.9 | 48 sticks (20 ft) | check laps |
| EXAMPLE · 6 mil vapor barrier | sq ft | 600 | 10 | 660 | 1 roll, 20×100 ft | add trench sides if beam is dug |
| EXAMPLE · 8×8×16 CMU | pcs | 342 | 5 | 359.1 | 360 | net of window |
| EXAMPLE · #4 vertical @ 48 in | 8 ft pcs | 11 | 0 | 11 | 6 sticks (20 ft) | by cut pattern |
Three things to notice: every line has a unit, waste is out in the open, and there isn’t a single price on the page.
Your sheet
| Item | Unit | Measured qty | Waste % | Qty with waste | Order | Note |
|---|---|---|---|---|---|---|
Before you move on to Chapter 2, check:
- Did every dimension come from a plan or a tape? If you assumed one, mark it ASSUMED.
- Does every line have a unit?
- Did you round up to the unit the supplier sells?
- Did you list what you couldn’t measure? That list belongs in the estimate too.
In Chapter 2 we take this same sheet and put prices on it, using your numbers, not someone else’s.