How to Estimate Crack Filler Before an Epoxy Job
Length, width, and depth explained — and why measuring at the wrong point leaves you short mid-repair.
Crack filler volume comes down to length × width × depth — but measuring at the wrong point on either width or depth is the easiest way to underestimate it. Measure width at the crack’s widest point and depth with a probe, not a guess, then let the Concrete Crack Repair Calculator handle the math and cartridge count.
How to read the inputs
Crack Length
- Total length of crack to fill, in ft or m — add up multiple cracks if you’re doing several in one job
Crack Width
- Measure at the widest point, not an average — cracks taper, and underestimating width is the most common way to run short
Crack Depth
- Use a nail or thin probe to feel where the crack actually bottoms out — it's almost always deeper than it looks from the surface
Waste Allowance
- Defaults to 15% — push it higher for an irregular or heavily tapered crack that won’t fill as predictably as a straight line
Worked example
A 12 ft crack, measured at 5 mm wide and 15 mm deep (the calculator’s own default width and depth), with the standard 15% waste allowance: raw volume = 12 ft (3,657.6 mm) × 5 mm × 15 mm ÷ 1,000 = 274.3 mL, plus 15% waste = 315 mL (10.7 fl oz). That rounds up to 2 standard 300 mL cartridges, or 1 twin-pack 600 mL cartridge.
Try it with your own crack
Enter length, width, and depth — width and depth default to typical values you can adjust.
Full result gives the volume needed and cartridge counts in your preferred units.
Open the live calculator →Common mistakes
- Measuring width at a typical-looking spot instead of the widest point along the crack
- Guessing depth instead of probing it — depth has a direct, linear effect on the volume needed
- Not adding enough waste allowance for an irregular or heavily tapered crack
- Ordering the exact calculated volume instead of rounding up — always keep at least one spare cartridge on hand
Frequently Asked Questions
Where should I measure crack width?
At the widest point along the crack, not an average or a spot that looks typical. Cracks taper and vary — measuring at the widest point avoids underestimating the volume needed and running short partway through.
How do I measure crack depth accurately?
Don’t eyeball it — insert a thin nail or probe into the crack to feel where it actually bottoms out. Cracks are very often deeper than they appear from the surface, and depth has a direct, linear effect on the volume needed.
How much waste allowance should I add?
The default is 15%, a reasonable starting point for a fairly regular crack. A more irregular or heavily tapered crack can eat more filler than a straight-line estimate accounts for, so consider pushing the allowance higher for those.
Should I round up to the next cartridge size?
Yes, always. Running out mid-crack forces an awkward pause and a visible cold joint in the repair. Order at least one extra cartridge as a buffer beyond the calculated volume.