Concrete Overage / Waste Calculator
Add a safety margin to any concrete order so you don’t run short mid-pour.
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Short answer
Most concrete pours should include 5 to 10% extra material beyond the calculated volume to cover spillage, uneven subgrade, and minor form movement. Irregular or hand-dug shapes like trench footings often warrant 10 to 15%, and complex or first-time DIY pours can justify 15 to 20%.
Typical waste percentage by job type
| Job type | Recommended overage |
|---|---|
| Flat slab on a graded, formed base | 5–8% |
| Footings and trench pours (irregular soil walls) | 10–15% |
| Curved, sloped, or first-time DIY pours | 15–20% |
| Small bag-mix jobs (posts, pads, steps) | 10% |
How to pick the right waste percentage
- Start with 10% as a reasonable default for most residential pours.
- Increase to 15% or more for trenches, footings dug directly into soil, or uneven ground where the exact volume is hard to predict.
- Decrease toward 5% for a well-formed, precisely measured slab on a flat, compacted base.
- Enter your base volume and waste percentage above to see the adjusted amount to order.
- When ordering ready-mix by the truck, round up to the nearest quarter or half yard since most suppliers have minimum order sizes.
Worked example
- Base volume needed
- 5.00 cubic yards
- Overage at 10%
- 5.00 × 0.10 = 0.50 cubic yards
- Total to order
- 5.00 + 0.50 = 5.50 cubic yards
Common mistakes
- Ordering the exact calculated amount with no buffer, then running short partway through the pour, which creates a weak cold joint.
- Adding a huge margin (25%+) out of caution, which wastes money on unused ready-mix or leftover bags.
- Forgetting that irregular, hand-dug excavations (like trench footings) almost always use more concrete than the on-paper dimensions suggest.
- Not accounting for the concrete truck’s minimum order size when a small waste allowance pushes the total just over a round number.
Assumptions
- Overage is applied as a flat percentage on top of the base volume you enter.
- Bag yields follow manufacturer averages: 80 lb = 0.60 ft³, 60 lb = 0.45 ft³, 50 lb = 0.375 ft³, 40 lb = 0.30 ft³.
- Cost estimate uses a flat price per cubic yard and does not include delivery fees or short-load surcharges.
- Does not account for supplier-specific minimum order sizes or truck capacity.
Frequently asked questions
How much extra concrete should I order?
5 to 10% extra covers most well-formed slab pours. Trenches, footings, and other irregular or hand-dug shapes should use 10 to 15% or more, since it’s hard to dig a perfectly uniform trench.
What happens if I run short of concrete mid-pour?
Running short mid-pour is one of the most common concrete mistakes. It forces a cold joint where old and new concrete meet, which is weaker and more visible than a continuous pour. Ordering a reasonable overage avoids this.
Do ready-mix trucks charge for leftover concrete?
Most suppliers charge for the full truck load you order, not just what you use, and some charge a short-load fee if you order less than their minimum. Ordering close to your actual need, with a modest buffer, avoids both wasted material and short-load fees.