How to Estimate Crack Filler Before an Epoxy Job
Length, width, and depth explained, plus why measuring at the wrong point leaves you short mid-repair.
Last updated August 15, 2026
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, because 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, when 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 and keeping 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, so 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.