How to use it
- Enter slab length in feet.
- Enter or adjust shrinkage rate (in/in).
- Click Calculate to see total shrinkage in inches and millimeters.
- Copy the values for your project plan.
What it does – The Concrete Shrinkage Calculator multiplies the slab length by the shrinkage rate you provide to give the estimated total shrinkage. The default rate is 0.0006 in/in (about 0.6 mm per meter), but you can edit it to match your mix, curing method, or humidity. Why it matters – Knowing how much a slab will contract helps you set proper joint spacing, add control‑joint allowances, and avoid cracking. How to read the output – The first number is the shrinkage in inches; the second converts that value to millimeters (1 in = 25.4 mm). Use the inches for U.S. construction specs and millimeters for metric drawings. The result is instant and requires no registration.
Pro tips
- Add a 10% waste allowance to the shrinkage total when planning joint gaps.
- Round up to the nearest 0.01 in to stay on the safe side.
- If you work in metric, use the mm result directly for reinforcement spacing.
- Double‑check the shrinkage rate against your supplier’s data sheet to avoid under‑estimating.
Real-life examples
- A residential contractor sizing control joints for a 24 ft driveway slab.
- A civil engineer verifying expansion joint gaps for a 150 ft warehouse floor.
- A DIY homeowner estimating crack‑control measures for a 12 ft patio.
Case study
John, a small‑business contractor, entered his 30 ft slab and the default 0.0006 in/in rate. The tool showed 0.018 in (0.46 mm) shrinkage, letting him add the right joint spacing and finish the project without costly cracks.