How Much Concrete for a 7x7 Hot Tub Pad?
Concrete needed
0.67 cubic yards
A 7 by 7 foot pad at four inches, with ten percent on top for waste. Compare the thickness table below.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Length7 ft
- Width7 ft
- Thickness4 in
- Waste allowance10 %
Concrete needed0.67 cubic yards
| Volume | 16.3 cu ft |
|---|---|
| Cubic yards before waste | 0.6 |
| Cubic yards with 10% waste | 0.67order to this number |
| Order in quarter yards | 0.75 cu yd |
| 60 lb bags, if bagging it | 40 |
| 80 lb bags, if bagging it | 30 |
The material list this produces
| Ready mix concrete, cubic yards | 0.75 |
|---|---|
| Rebar or mesh, sq ft of slab | 49 |
| Form lumber, linear ft | 28 |
Thickness compared
Thickness is the one number on this page worth arguing about, so here is the same slab at each of the usual four.
| Thickness | Concrete needed |
|---|---|
| 4 in | 0.67 cubic yards |
| 5 in | 0.83 cubic yards |
| 6 in | 1 cubic yard |
| 8 in | 1.33 cubic yards |
What else matters here
This is the one page here where the default thickness is probably wrong for the job. A hot tub pad carries a load that a patio never sees: a filled seven foot tub with people in it runs somewhere between 4,000 and 6,000 pounds, concentrated on a footprint of about fifty square feet.
Most manufacturers specify four inches minimum and many specify more, usually six inches with wire mesh or half inch rebar on twelve to sixteen inch centers. Read the tub's own manual before pouring, because a pad that fails under a filled tub is not a repair, it is a drain, a crane and a new pad.
The thickness table below is the point of this page. Six inches on a 7 by 7 is about half a yard more concrete than four inches, which at bag prices is roughly fifteen more bags. Against the cost of the tub it is not a number worth economizing on.
What this calculator assumes
- One cubic yard is 27 cubic feet. A 4 inch slab is one third of a foot thick, not 4.
- A 60 lb bag yields about 0.45 cubic feet and an 80 lb bag about 0.60. Bags are for small pours only; past about one cubic yard, ready mix is cheaper and far less work.
- Ready mix is usually sold in quarter yard steps with a short load fee below one yard.
Questions people ask
How thick should a hot tub pad be?
Four inches is the usual minimum and six inches with mesh or rebar is what many manufacturers specify. Check the manual for the tub, because the requirement is theirs, not the code's.
How much does a filled hot tub weigh?
A seven foot tub filled and occupied is commonly 4,000 to 6,000 pounds, sitting on about fifty square feet.
How many bags of concrete for a 7x7 hot tub pad?
About 40 sixty pound bags or 30 eighty pound bags at 4 inches. At the 6 inches many tubs want, it is around 60 and 45.
The concrete calculator takes any dimensions you like and hands back the same list.