Shed base: gravel or concrete
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The choice between a gravel shed pad and a concrete slab is drainage, movement, and what the local code calls a foundation. The quantity is the easy part, and it already lives on two calculators. This page puts the same footprint in both materials, then keeps frost and permits as the local questions they are. It does not pick a winner for a town it has not seen.
The same pad, two weights
Volume follows the box. Ten feet by 12 feet by 4 inches is 10 × 12 × 4 ÷ 324 = 1.48 cubic yards, 40.00 cubic feet, and 1.13 cubic meters. The material changes the weight. The gravel shed foundation calculator starts a rectangle at 1,920 kg/m³, which that page states as 1.62 short tons per cubic yard. The 10 by 12 example is 2.40 short tons and 2.17 tonnes. The concrete slab calculator starts at 2,400 kg/m³, about 2.02 short tons per cubic yard. The same 1.48 cubic yards is 3.00 short tons and 2.72 tonnes. The slab page’s own 12 by 16 foot example at 4 inches is 2.37 cubic yards and 4.79 short tons, which is the same density on a larger pad.
The shed base size calculator starts from the floor and adds a border on every side. Pad length is floor length plus two borders. A 10 by 12 floor with a 1 foot border is 12.00 by 14.00 feet (3.66 by 4.27 meters). At 4 inches and 1,920 kg/m³ that pad is 2.07 cubic yards, 56.00 cubic feet, 1.59 cubic meters, 3.36 short tons, and 3.04 tonnes. A border of 0 reproduces the foundation page’s 1.48 cubic yards and 2.40 short tons. A 6 inch border is the 11 by 13 foot pad, 1.77 cubic yards and 2.86 short tons. None of those gravel lines includes a 10 percent loose-order allowance. The foundation page says to add that yourself if the quarry sells loose stone for a compacted finish.
The concrete of the bordered footprint is the slab tool, not a second mode on the gravel page. Twelve by 14 feet at 4 inches is the same 2.07 cubic yards. At 2,400 kg/m³ the weight is 4.20 short tons and 3.81 tonnes. The slab calculator does not add gravel under the concrete, and the gravel calculators do not add a slab on top. If the job is stone and then concrete, run both tools.
| Pad | Volume | Gravel | Concrete |
|---|---|---|---|
| 10×12 ft, no border | 1.48 yd³ · 1.13 m³ | 2.40 short tons · 2.17 t | 3.00 short tons · 2.72 t |
| 11×13 ft, 6 in border | 1.77 yd³ | 2.86 short tons · 2.59 t | Type 11 by 13 on the slab calculator |
| 12×14 ft, 1 ft border | 2.07 yd³ · 1.59 m³ | 3.36 short tons · 3.04 t | 4.20 short tons · 3.81 t |
What each base is good at
The gravel tools start a rectangle at 1,920 kg/m³ and call it a crushed-stone-and-fines blend. That pad can be re-leveled if a corner settles, and water can leave the edges if the surface does not pond against the skids. It is still a dense base, not the open #57 trench in the French drain guide. A pad that pumps mud is a failed subgrade.
Concrete is a rigid slab at the slab calculator’s 2,400 kg/m³. It gives a hard floor, and the weight is the higher of the two lines above. Water does not pass through the slab, so the surface has to slope away from the shed and from any wall the shed touches. The slab page’s thickness notes treat 4 inches as the light worked example and thicker slabs as the driveway and heavy end. Those are planning bands on that page, not a shed code. A turned-down edge, a pier, or a footing is the concrete footing calculator. Typing a deeper number into the slab tool counts a thicker slab, not a footing.
A gravel pad that settles can be lifted and re-stoned. A slab that settles cracks. Neither material fixes a subgrade that is pumping. Circles and polygons stay on the foundation page, where the triangle and polygon tools open at 1,600 kg/m³ until you type 1920.
Frost
Frost depth is local. The text that was readable for this page is the 2003 International Residential Code, Chapter 4, on the ICC site. Section R403.1.4 says all exterior footings shall be placed at least 12 inches (305 mm) below the undisturbed ground surface, and that where it applies they also follow R403.1.4.1 and R403.1.4.2. Section R403.1.4.1 says foundation walls, piers, and other permanent supports shall be protected from frost by extending below the frost line in Table R301.2(1), or by the frost-protected shallow foundation in R403.3, or by ASCE 32-01, or by bearing on solid rock. Footings shall not bear on frozen soil unless that frozen condition is permanent. The frost line in the table is filled in by the jurisdiction. This page does not print a depth for your town.
A gravel pad is not on that list of frost methods. Four inches of stone at grade does not extend a footing below the frost line. If the shed needs the protection in R403.1.4.1, the pad thickness on the gravel calculator is the floor base, and the footing is a separate dig. The same is true of a 4 inch slab. Slab thickness and frost depth are different numbers.
The 2003 text has an exception. Freestanding accessory structures with an area of 400 square feet (37 m²) or less, and an eave height of 10 feet (3048 mm) or less, shall not be required to be protected. A 10 by 12 floor is 120 square feet, so the area is under that figure if the eaves also stay within 10 feet and the shed is freestanding. A later code, or a local amendment, may not keep that exception. The sentence is about frost protection. It does not set the gravel depth, and it does not approve the pad.
Size and permits
The size calculator adds the border on each side, so a 1 foot border adds 2 feet to the length and 2 feet to the width. Order the pad when the stone or the slab sticks out past the walls. A border of 0 is the floor itself. A ramp is a second rectangle.
Permits are the building department’s. Floor area, height, and whether the shed sits on a permanent foundation are the usual questions, and the cutoff is not one national number this page can cite beyond the 2003 frost exception above. There is no price comparison here, because a local fee and a local yard price were not opened and will not be invented. Call the department that issues the permit where the shed will stand, and use the calculators for the material once the pad size is the one they will accept.
Sources
- 2003 International Residential Code, Chapter 4, sections R403.1.4 and R403.1.4.1, including the 12 inch minimum footing depth, the local frost line, and the accessory-structure exception of 400 square feet and 10 feet of eave height. A later edition may differ.
- Quantities are this site’s own tools: the shed foundation calculator at 1,920 kg/m³, the shed base size calculator for the border, and the concrete slab calculator at 2,400 kg/m³. The 10 by 12 and 12 by 14 weights were computed with those densities and the same yard conversion the order line uses.
Frequently asked questions
How much gravel is a 10 by 12 shed pad?
Ten by 12 feet at 4 inches and 1,920 kg/m³ is 1.48 cubic yards, 2.40 short tons, 2.17 tonnes, and 1.13 cubic meters. A border of 0 on the shed base size calculator matches those numbers. A 1 foot border on every side makes 12.00 by 14.00 feet: 2.07 cubic yards and 3.36 short tons. The border is added to both the length and the width.
How much concrete is the same 10 by 12 pad?
The volume is the same 1.48 cubic yards, because 10 × 12 × 4 ÷ 324 does not change with the material. At the slab calculator’s 2,400 kg/m³ the order line is 1.13 cubic meters, 3.00 short tons, and 2.72 tonnes. A 12 by 14 foot slab at 4 inches, the footprint of the 1 foot border, is 2.07 cubic yards and 4.20 short tons at 2,400 kg/m³. The slab tool does not add a gravel base under that concrete. Type the slab you will pour.
Which one drains?
A compacted crushed-stone pad, which is what the shed tools start at 1,920 kg/m³, sheds water off a shaped surface and can be re-leveled if it settles. It is not the open #57 envelope in a French drain, and water does not disappear through a dense base the way it moves through clean stone. A concrete slab does not drain through the concrete. Water has to leave the surface. The slab calculator does not apply a slope for you.
Does a gravel pad replace a frost footing?
No. The 2003 IRC section R403.1.4 places exterior footings at least 12 inches below undisturbed ground. Section R403.1.4.1 protects permanent supports by extending them below the local frost line in Table R301.2(1), or by the other methods that section lists. A gravel pad is not one of those methods. The frost line is the local table, and this page does not invent one.
Is a small shed exempt from frost protection?
In the 2003 IRC text that was readable, freestanding accessory structures of 400 square feet or less, with an eave height of 10 feet or less, are not required to be frost-protected. A 10 by 12 floor is 120 square feet, which is under that 400 square foot figure, and the exception still requires the structure to be freestanding and within the height limit. A city may have adopted a later code or deleted the exception. The exemption is about frost protection of the supports. It is not a statement that the pad can be any thickness, and it is not a permit.
Do I need a permit?
Ask the local building department. Permit rules follow floor area, height, and whether the shed is on a permanent foundation, and they are not the same from one county to the next. This page does not list a city, a fee, or a cutoff that would apply where you are. The 2003 IRC frost exception above is a model-code sentence, not a local approval.
Where are the yards?
Gravel for the rectangle, circle, and other shapes is the gravel shed foundation calculator. Floor size plus a border is the shed base size calculator. A concrete slab of the same footprint is the concrete slab calculator. A turned-down edge or a pier is the concrete footing calculator, not a thicker number typed into the slab. This page does not repeat those widgets.