Building a garden shed is an exciting project, but getting the base right is crucial. A solid concrete base will keep your shed level, dry, and stable for years to come. The big question is: how much concrete do you actually need?
Don’t worry – working out concrete quantities isn’t as tricky as it sounds. Let’s break it down into simple steps.
Why Your Shed Needs a Proper Base
Before we dive into calculations, let’s talk about why concrete matters. A proper base stops your shed from sinking into soft ground, prevents damp from creeping up through the floor, and keeps everything square and level.
Without a good foundation, even the best shed can start to lean, doors won’t close properly, and you might end up with water damage. It’s worth doing once and doing it right.
Measuring Your Shed Base
The first step is working out the size of your concrete slab. This depends on your shed size, but here’s the golden rule: make your base slightly bigger than your shed.
Add about 50-75mm (2-3 inches) to each side of your shed dimensions. So if your shed is 2m x 3m, your concrete base should be roughly 2.15m x 3.15m. This extra space gives you room for error and helps water drain away from the shed walls.
How Thick Should Your Concrete Be?
For most garden sheds, a concrete base should be 100mm (4 inches) thick. This gives you plenty of strength without wasting concrete.
If you’re planning to store particularly heavy items like a ride-on mower or workshop equipment, you might want to go up to 125mm (5 inches) thick. But for standard garden storage, 100mm is perfect.
The Simple Calculation
Here’s the easy way to work out how much concrete you need:
Length (in metres) × Width (in metres) × Thickness (in metres) = Volume in cubic metres
Let’s use our example shed base:
- Length: 3.15m
- Width: 2.15m
- Thickness: 0.1m (that’s 100mm)
3.15 × 2.15 × 0.1 = 0.68 cubic metres
Always add an extra 10% to your calculation for wastage and to make sure you don’t run short. So 0.68 + 10% = 0.75 cubic metres.
Using Our Concrete Calculator
If maths isn’t your strong point, don’t worry. Our handy concrete calculator does all the work for you. Just pop in your measurements and it’ll tell you exactly how much concrete to order.
The calculator even accounts for wastage, so you get an accurate figure every time.
What Type of Concrete Do You Need?
For shed bases, you want a standard C20 concrete mix. This has the right strength for the job without being over the top. According to the UK Planning Portal’s building regulations guidance, all buildings require adequate concrete foundations that transmit loads safely to the ground, and C20 concrete is ideal for lightweight domestic applications like shed bases.
Preparation Tips
Before your concrete arrives, make sure you’re ready:
- Mark out your area and check it’s square using the 3-4-5 triangle method
- Dig out the area to the right depth (usually 150mm to allow for concrete plus hardcore)
- Put down a layer of hardcore or MOT Type 1 and compact it well
- Set up your formwork (the wooden frame that holds the concrete)
- Have your tools ready: rake, shovel, float, and spirit level
Getting Your Concrete Delivered
Ready-mix concrete is much easier than mixing bags yourself, especially for anything bigger than a small shed base. A typical garden shed base uses between 0.5 and 1.5 cubic metres of concrete – perfect for our mini-mix service.
When you call us, we’ll need to know:
- The volume of concrete you need
- Your postcode for delivery
- When you want it delivered
- Access details (can our truck get close to your garden?)
The Bottom Line
Working out concrete quantities doesn’t have to be complicated. Measure your shed, add a bit extra, multiply by 0.1m for thickness, and add 10% for wastage.
For a typical 2m x 3m shed, you’re looking at about 0.75 cubic metres of concrete. Use our concrete calculator to double-check your figures, and you’ll have everything sorted.
Remember, it’s always better to have slightly too much concrete than not enough. You can’t pop to the shops halfway through laying a slab!
Ready to get started? Give us a call and we’ll help you work out exactly what you need for your shed base project.
