Calculator
Enter your dimensions, choose options, then calculate.
Example data table
| Scenario | Inner Ø | Thickness | Height | Blocks (with 8% waste) | Outer Ø |
|---|---|---|---|---|---|
| Compact seating spot | 90 cm | 10 cm | 30 cm | 36 | 110 cm |
| Family garden circle | 120 cm | 12 cm | 40 cm | 54 | 144 cm |
| Wide patio feature | 150 cm | 15 cm | 45 cm | 72 | 180 cm |
These rows are examples. Your results update from your own inputs.
Formula used
- rᵢ = Dᵢ / 2 (inner radius)
- rₒ = rᵢ + t (outer radius)
- Dₒ = Dᵢ + 2t (outer diameter)
- C = πD (circumference)
- A_floor = πrᵢ² (inner area)
- A_ring = π(rₒ² − rᵢ²) (annulus area)
- V_wall = A_ring × h (wall volume)
- Blocks/course ≈ Cₒ ÷ (Lᵦ + joint)
- Courses ≈ h ÷ (Hᵦ + vJoint)
- Blocks ≈ ceil(course) × ceil(courses)
- Caps ≈ ceil(Cₒ ÷ (L_c + joint))
- With waste: total × (1 + waste%)
- Base volume = π(rₒ + overhang)² × depth
All calculations are performed in meters internally, then converted to your chosen unit system.
How to use this calculator
- Select Metric or Imperial units to match your tape measure.
- Enter inner diameter, wall thickness, and wall height.
- Enter your block size and joint gaps for a better estimate.
- Enable cap stones and gravel base if you plan to use them.
- Add waste percentage and costs for a budget preview.
- Press Calculate to show results above the form.
- Use Download CSV or Download PDF for sharing.
Planning notes for a fire pit ring
Choosing a practical ring diameter
A comfortable cooking and seating layout starts with the inner diameter. Smaller rings warm quickly and conserve fuel, while larger rings provide better airflow and space for longer logs. A common backyard range is 90–150 cm, but choose what fits your site and seating. Use the outer diameter to confirm patio clearance, edging, and furniture spacing. If children will be nearby, consider a wider safety buffer around the outside edge.
Understanding thickness and height
Wall thickness controls stability and heat shielding. A thicker ring increases material volume and outer circumference, which directly affects block count. Wall height influences draft and ember control; taller rings reduce blow‑out but can make access harder for grilling. Use the courses estimate to check whether your chosen block height lands on a clean number of layers.
Estimating blocks with joints and waste
Block quantity depends on circumference divided by block length plus the horizontal joint gap. Even small joint changes compound around the circle, so measure a real sample with spacers. The calculator rounds up per course and rounds up courses, then applies a waste allowance for cuts, breakage, and color matching. For angled cuts on straight blocks, increase waste slightly.
Cap stones and finish planning
Caps improve comfort for hands, reduce sharp edges, and protect the top course from weather. The cap estimate uses outer circumference and cap length, then adds the same joint gap. If you plan a staggered pattern, confirm the visible overhang still covers joints below. Pair caps with heat‑rated adhesive or mortar as recommended by the product manufacturer.
Base layer, drainage, and budgeting
A compacted gravel base helps leveling, reduces frost movement, and improves drainage under the ring. Base volume is calculated from the radius plus overhang, multiplied by base depth. Pricing becomes clearer when you enter per‑unit material costs and compare totals with and without caps or base. Export the CSV for supplier quotes and keep the PDF for the simple build day checklist.
FAQs
What diameter works for a small garden patio?
Many patios suit a 90–120 cm inner diameter. It leaves space for compact seating and keeps heat close. Confirm the outer diameter plus clearance fits your paving or lawn edge.
Should I use a metal liner inside the ring?
A steel liner reduces direct flame contact with masonry and can extend wall life. Ensure it matches the inner diameter and allows airflow. Keep a gap so heat does not crack blocks.
How do I set waste allowance?
Use 5–10% for standard blocks and gentle curves. Raise it for straight blocks that need frequent cuts, mixed colors, or many cap corners. The calculator applies waste after rounding up courses and blocks.
Do I need a gravel base?
A compacted gravel base improves leveling and drainage, especially on soil. It also reduces frost heave in cold regions. If your site is stable concrete, you may disable the base option and focus on ring dimensions.
Why do my block counts seem high?
Counts rise when joint gaps increase, wall height adds courses, or outer circumference grows with thickness. Check block length and verify units. Remember the tool rounds up per course and adds waste for practical purchasing.
Can I download results for suppliers?
Yes. Use the CSV for pricing and quantity checks, and the PDF for a quick site reference. The downloaded file reflects your current inputs, including unit system, waste factor, and optional caps or base.