Mulch calculator / Measured oval beds
Oval Mulch Calculator
Measure the full length and width, then choose the outline. An ellipse and a straight-sided oval do not cover the same ground.
Mulch for the layer you plan to add
— cu ft
— cu yd
— whole bags
Enter the full measured dimensions and added depth. Nothing is estimated from a photograph.
Same measurements, different bag counts
A 12 ft × 8 ft ellipse has about 75.40 sq ft of area. At a user-chosen 3-inch added layer, with no excluded ground, it needs 18.85 cu ft: 10 whole bags if each package contains 2 cu ft.
A straight-sided oval with those same full dimensions has about 82.27 sq ft: a 4 ft × 8 ft middle plus two semicircles. The same added layer needs 20.57 cu ft, or 11 of those bags. Treating either outline as a 12 ft × 8 ft rectangle would give 24 cu ft and 12 bags. These are worked measurements, not a recommended depth or product.
Two measurements are enough only for the right outline
For an ellipse, half the full length and half the full width are the two semi-axes. Area is π × those semi-axes. Iowa State University Extension's garden measurement guide identifies this as an oval-bed method; Harvey Mudd College's ellipse explanation states the relationship between full axes and semi-axes.
For a straight-sided oval, width is the diameter of each semicircular end. The straight middle is full length minus width. Its rectangle plus the two half-circles gives area = (length − width) × width + π × (width ÷ 2)², following the stadium geometry described by Wolfram MathWorld. This does not apply to every rounded rectangle.
Subtract measured unmulched ground from that area. Multiply the remainder by added depth in the same units: inches ÷ 12 for feet, or centimetres ÷ 100 for metres. Divide cubic feet by 27 for cubic yards; multiply cubic metres by 1,000 for litres. Divide the combined volume by your printed package volume and round up once. The Extension mulch-volume guide supports the area/depth method and whole-bag conversion. These sources establish geometry and units, not supplier prices or a safe depth for every plant.
If the outline bulges unevenly, bends like a kidney, or has several separate spans, use the measured width-station worksheet or scaled grid-sketch calculator. Do not force an irregular bed into either oval formula. For several beds, keep each measured estimate and combine their material quantities before rounding the order.
Oval-bed questions
Do I enter the full length or half the length?
Enter the full edge-to-edge length and full perpendicular width. The ellipse calculation halves both measurements internally; entering radii would make the area four times too small.
Are all oval beds ellipses?
No. An ellipse curves continuously. A straight-sided oval has a rectangular middle and two semicircular ends. A kidney-shaped or uneven outline needs a measured grid or width-station estimate instead.
Can I subtract a planter or stepping stones?
Yes. Enter their measured total area in the displayed square units. Count each piece once and include only ground inside the bed. The calculator checks the total against the bed area but cannot verify placement or overlap.
Does this choose a mulch depth or an extra allowance?
No. You enter the layer you plan to add and the volume printed on your bag. No depth recommendation, waste factor or settlement allowance is included. Whole-bag rounding is shown separately.