KORA takeoff rarely goes wrong because of a multiplication. It goes wrong because a scale wasn't checked, a wall was measured twice, or a drawing revision was missed. Here are the mistakes we see most often, with worked examples, and a simple way to avoid each one.
The examples use a small 28' x 40' house, walls at 16" o.c. with an 8'-1" height, and 10% waste. These values are for the example only: use your own.
1. A scale read too quickly and never confirmed
The scale written on the sheet isn't always the scale of the drawing you're measuring. One sheet can hold a 1/4" plan and a 1/2" detail, and a PDF may have been printed at a different size than the original.
If you measure at 1/8" a plan drawn at 1/4", every length doubles and every area is multiplied by four:
| Right scale (1/4") | Wrong scale (1/8") | |
|---|---|---|
| House dimensions | 28' x 40' | 56' x 80' |
| Area | 1,120 sq. ft | 4,480 sq. ft |
The error is big here, so it's easy to spot. It's more dangerous when the gap is small, for example a PDF reduced to 95%: nothing jumps out.
How to avoid it: confirm the scale of every sheet, then check it against a known dimension (see mistake 7).
2. The same wall measured twice, with two lengths
You measure the exterior walls for framing, then again for drywall, then again for insulation. Each time you click in a slightly different spot. Result: 136 lin. ft for framing, 131 lin. ft for drywall.
| 1/2" drywall 4x8, 1 side, 8'-1" | Math | Sheets |
|---|---|---|
| With 136 lin. ft | 136 × 8.083 = 1,099 sq. ft ÷ 32 = 34.4 × 1.10 = 37.8 | 38 |
| With 131 lin. ft | 131 × 8.083 = 1,059 sq. ft ÷ 32 = 33.1 × 1.10 = 36.4 | 37 |
One sheet isn't a big deal on its own. The problem is that your quantities no longer agree with each other, and a drawing change must be fixed three times.
How to avoid it: measure each wall once, and have drywall, insulation, vapour barrier and paint reuse that length.
3. Rounding item by item
If you count studs wall by wall, each wall rounds up, adds its waste, then rounds up again. The small roundings add up.
Four walls: 11'-5", 9'-10", 7'-3" and 5'-4" (total 33'-10"). Rule: (length ÷ spacing, rounded up) + 1 per wall, then + 10% waste, rounded up.
| Method | Math | Studs |
|---|---|---|
| Wall by wall | 11 + 10 + 8 + 6 | 35 |
| On the total | 33.833 × 12 ÷ 16 = 25.4 → 26, + 4 ends = 30, × 1.10 = 33 | 33 |
Two extra studs out of 33, about 6%, across every wall in the project. The same effect hits drywall sheets, OSB and bags.
How to avoid it: add up all walls of the same type first, calculate, then round once.
4. Waste counted twice, or not at all
Waste can slip in at two places: in the takeoff formula and in the estimate ("I'll add 10% to be safe"). Or nowhere, if everyone thinks someone else did it.
| OSB 4x8, 136 lin. ft x 8'-1" (1,099 sq. ft) | Math | Sheets |
|---|---|---|
| No waste | 1,099 ÷ 32 = 34.4 | 35 |
| Waste once | 34.4 × 1.10 = 37.8 | 38 |
| Waste twice | 34.4 × 1.10 × 1.10 = 41.6 | 42 |
Four more sheets on a single wall type: a little over 10% on that material.
How to avoid it: pick one place for waste (usually the takeoff formula) and write it into your method.
5. Opening rules that change from project to project
Should windows be deducted from drywall? Both answers can be defended. Many estimators don't deduct small openings, because offcuts rarely make up for them; others deduct everything. The mistake is switching rules between projects.
Example: 12 windows at 3' x 4' = 144 sq. ft, or 4.5 sheets of 4x8 (about 5 with 10% waste). If one project deducts them and the next doesn't, your price per square foot no longer compares.
How to avoid it: write your rule down (e.g. "we don't deduct openings in drywall; we deduct large openings such as a garage door") and apply it everywhere.
6. Mixed units
Two common traps:
- Inches typed as decimals. 4'-9" isn't 4.9 ft, it's 4.75 ft. That's a 3.2% error, repeated on every dimension typed that way.
- Cubic yards and cubic metres. A 28' x 40' slab at 4" is 373 cu. ft, or 13.8 cu. yd, or 10.6 m³. Order "10.6" from the supplier while thinking in yards and you're short about 3.3 cu. yd, nearly a quarter of the slab.
| Slab 28' x 40' x 4" | Value |
|---|---|
| Volume | 1,120 sq. ft × 0.333 ft = 373 cu. ft |
| In cubic yards | 373 ÷ 27 = 13.8 cu. yd |
| In cubic metres | 373 × 0.0283 = 10.6 m³ |
How to avoid it: keep the unit written next to every quantity, and let your tool convert units rather than doing it by hand.
7. Never checking against a known dimension
Before measuring a sheet, measure a dimension written on the drawing: the overall length of the house, a garage door opening. If you read 39'-6" where the drawing says 40'-0", your scale or your print has a problem, and every measurement on that sheet will too.
How to avoid it: one check measurement per sheet, at the start. If it's off by more than a few inches, recalibrate the scale with that dimension.
8. Measuring an old drawing revision
You started on the "For tender" issue, then an addendum changed the basement wall height. If your takeoff stays on the old version, every quantity that depends on that height is wrong: concrete, formwork, insulation, drywall.
How to avoid it: record the revision and date of each plan set in your takeoff. When an addendum arrives, keep a copy of the takeoff from before, make the changes, and compare both totals to see what moved.
9. Forgetting what's on other sheets
The floor plan gives lengths, but not everything. Wall height is often on the section. Slab thickness, under-slab insulation and rebar are in the details. Door and window counts are in the schedules. General notes sometimes call for a more expensive product.
How to avoid it: page through the whole set before measuring, and note for each trade the sheets that concern it (sections, details, schedules, specifications on the drawings).
A checklist before you send the price
- Scale confirmed on every sheet, and one known dimension checked.
- Each wall measured only once.
- Totals added before rounding.
- Waste applied in one place only.
- Same opening rule as your other projects.
- Units written next to every quantity.
- Right drawing revision, addenda included.
- Sections, details, schedules and notes reviewed.
How KOR helps avoid these mistakes
In KOR, the scale found on each sheet always has to be confirmed, and you can calibrate it with a known dimension. A wall measured once can be reused by the drywall, insulation and paint items: correct the wall and everything follows. Templates calculate on the item's total, with a single rounding and waste applied once, using formulas you can read and edit. Quantities display in imperial or metric, converted by the app. Takeoff versions (V1, V2 after addendum…) can be compared to see which quantities change, and specification notes can be boxed right on the drawing.
No tool replaces an estimator's eye. But a written method, applied the same way on every project, prevents most of the mistakes on this list.