How Much Does a 1.5 Cubic Foot Bag of Soil Weigh?

How much does a 1.5 cubic foot bag of soil weigh? A 1.5 cubic foot bag of topsoil weighs around 60 to 80 lb, and a 1.5 cubic foot bag of potting mix weighs around 20 to 40 lb. The difference comes from bulk density, because topsoil is far heavier than potting mix for the same volume.

Why one bag size gives two very different weights

A bag size tells you volume, not weight. Topsoil is dense and often damp, so the same 1.5 cubic feet weighs much more than light potting mix. The site FAQ gives the split plainly: topsoil 60 to 80 lb, potting mix 20 to 40 lb. Use the Topsoil Weight to Cubic Feet Calculator to check your own bag before you buy.

The formula for bag weight

Weight equals volume times bulk density. Volume is the bag size in cubic feet. Bulk density is the weight of one cubic foot in lb per cubic foot. For the reverse check, volume equals weight divided by bulk density. The site worked example uses 53 lb per cubic foot for bagged topsoil, inside the site range of 50 to 55 lb per cubic foot. A 40 lb bag at that density holds about 0.75 cubic feet.

Worked example 1: a 1.5 cubic foot bag of topsoil

Weight is 1.5 times 53, which is 79.5 lb, shown as about 80 lb. That figure sits at the top of the site FAQ range of 60 to 80 lb. At the site density range, weight is 75 to 82.5 lb, because 1.5 times 50 equals 75 and 1.5 times 55 equals 82.5. The FAQ range is wider at the low end, because it covers drier or lighter topsoil, and its low end implies density as low as 40 lb per cubic foot, because 60 divided by 1.5 equals 40. Give the full 60 to 80 lb range. In metric units, 1.5 cubic feet equals 42.5 litres, and 60 to 80 lb equals 27.2 to 36.3 kg.

Worked example 2: a 1.5 cubic foot bag of potting mix

The site FAQ gives 20 to 40 lb for potting mix in a 1.5 cubic foot bag. That range implies density of 13.3 to 26.7 lb per cubic foot, because 20 divided by 1.5 equals 13.3 and 40 divided by 1.5 equals 26.7. That implied range is the only potting mix density on the site page. In kg, 20 lb equals 9.1 kg and 40 lb equals 18.1 kg. The midpoint is 30 lb, which is 13.6 kg. At the midpoint, topsoil weighs about 80 lb and potting mix weighs about 30 lb for the same volume.

Weight by material for a 1.5 cubic foot bag

Material	Volume	Weight in lb	Implied density in lb per cubic foot
Topsoil	1.5 cubic feet, 42.5 litres	60 to 80 lb	40 to 53 lb per cubic foot, 50 to 55 lb per cubic foot site range
Potting mix	1.5 cubic feet, 42.5 litres	20 to 40 lb	13.3 to 26.7 lb per cubic foot

Weight by bag size for topsoil

Bag size	Volume in litres	Weight at 53 lb per cubic foot	Bags per cubic yard
0.75 cubic feet	21.2 litres	39.8 lb, about 40 lb	36 bags
1 cubic foot	28.3 litres	53 lb	27 bags
1.5 cubic feet	42.5 litres	79.5 lb, about 80 lb	18 bags
2 cubic feet	56.6 litres	106 lb	13.5 bags exact, 14 bags buyable

Check the table: 0.75 times 53 equals 39.75 lb, shown as 39.8 lb, and 2 times 53 equals 106 lb. For bags per cubic yard, 27 divided by 0.75 equals 36 bags, 27 divided by 1.5 equals 18 bags, and 27 divided by 2 equals 13.5 bags exact, so buy 14 bags rounded up. The 0.75 cubic foot row is the 40 lb bag in the site worked example, with 34 to 38 bags per cubic yard at the full site density range.

Why some pages claim 120 lb for a 1.5 cubic foot bag

Some pages give 120 lb for a 1.5 cubic foot bag. That figure is correct arithmetic for a different density, and it is wrong for bagged topsoil at site density. It uses about 80 lb per cubic foot, because 1.5 times 80 equals 120 lb. That density is bulk dense density, not bagged damp density. A range of 74 to 110 lb per cubic foot gives 111 to 165 lb. Ask for the density before you accept a weight, and keep the two density families apart.

Moisture changes the weight of the same bag

Dry soil can be 30 percent lighter, and that is the only moisture figure the site page states. Work it through as an illustration only, labelled as such. Dry density at 30 percent lighter than 53 lb per cubic foot is 53 times 0.70, which is 37.1 lb per cubic foot. A 1.5 cubic foot bag at that dry density weighs 1.5 times 37.1, which is 55.65 lb, shown as about 56 lb. A 40 lb bag of dry soil at 37.1 lb per cubic foot holds 1.08 cubic feet, while a moist 40 lb bag at 53 lb per cubic foot holds about 0.75 cubic feet.

Read the bag label the right way

The volume printed on the bag controls the bag count, and the weight printed on the bag does not control volume. Count bags by the volume on the label, then use weight only for the lift and load check. Bag labels may state volume before compression, so allow for settling. Check the volume and the material name, and compare the printed weight with the table in this guide.

How many 1.5 cubic foot bags make a cubic yard

A cubic yard holds 27 cubic feet, so the count is 27 divided by 1.5, which is 18 bags. That count is the same for topsoil and for potting mix, because it depends on volume, not on weight. For topsoil, 18 bags at 60 to 80 lb each give 1080 to 1440 lb. For potting mix, 18 bags at 20 to 40 lb each give 360 to 720 lb. That total matches the 40 lb bag count, because 36 times 40 equals 1440 lb.

Worked example 3: a small bed filled with 1.5 cubic foot bags

A bed that needs 9 cubic feet of topsoil needs 9 divided by 1.5, which is 6 bags. The weight is 6 bags at 60 to 80 lb each, which is 360 to 480 lb. The same bed filled with potting mix needs the same 6 bags, but the weight is 120 to 240 lb. Use the Topsoil Calculator for your own bed volume, the Soil Calculator for weight, the Garden Volume Calculator for litres, and the Potting Soil Calculator for pots. For more guides, use the Guides page.

Common mistakes

1. Using one weight for every material. Check the material name first.
2. Using 120 lb for bagged topsoil. That figure uses about 80 lb per cubic foot, which is bulk dense density.
3. Treating 80 lb as the only topsoil figure. The site FAQ gives 60 to 80 lb.
4. Treating a 40 lb bag as a fixed volume. It holds about 0.75 cubic feet when moist and 1.08 cubic feet when dry.
5. Buying 13.5 bags. You cannot buy 13.5 bags, so buy 14 bags rounded up.
6. Counting bags by weight instead of volume. Volume controls the count.
7. Ignoring volume before compression. Bag labels may state volume before compression.
8. Ignoring moisture. Dry soil can be 30 percent lighter, so plan for damp soil.
9. Mixing units in one sum. Keep cubic feet with lb per cubic foot.
10. Forgetting the total load. Eighteen bags of topsoil weigh 1080 to 1440 lb for a cubic yard.

Use the calculator for your own bag

Put your own bag figures into the Topsoil Weight to Cubic Feet Calculator. Enter the weight from the label, use the site density range of 50 to 55 lb per cubic foot for bagged topsoil, and read the volume that weight gives.

Frequently asked questions

Q: How much does a 1.5 cubic foot bag of soil weigh?
A: A 1.5 cubic foot bag of topsoil weighs around 60 to 80 lb, and a 1.5 cubic foot bag of potting mix weighs 20 to 40 lb. The difference comes from bulk density.

Q: How much does a 1.5 cubic foot bag of topsoil weigh in kg?
A: A 1.5 cubic foot bag of topsoil weighs 27.2 to 36.3 kg. At 53 lb per cubic foot, it weighs 79.5 lb, which is 36.1 kg.

Q: Why do some pages say a 1.5 cubic foot bag weighs 120 lb?
A: Those pages use about 80 lb per cubic foot, because 1.5 times 80 equals 120 lb. That is bulk dense density, not bagged density. Site bagged density is 50 to 55 lb per cubic foot.

Q: How many 1.5 cubic foot bags make a cubic yard?
A: Eighteen bags make a cubic yard, because 27 divided by 1.5 equals 18. For topsoil, those 18 bags weigh 1080 to 1440 lb in total. For potting mix, they weigh 360 to 720 lb in total.

Q: How much does a 40 lb bag of topsoil weigh in cubic feet?
A: A 40 lb bag holds about 0.75 cubic feet when moist at 53 lb per cubic foot, because 40 divided by 53 equals 0.75 when rounded. That is 21 litres. Dry, at 37.1 lb per cubic foot, it holds 1.08 cubic feet.

Q: Does dry soil weigh less than damp soil in the same bag?
A: Yes. Dry soil can be 30 percent lighter. At 37.1 lb per cubic foot, a 1.5 cubic foot bag weighs about 56 lb. Plan for damp soil when you lift and load.

A 1.5 cubic foot bag of topsoil weighs 60 to 80 lb, and a 1.5 cubic foot bag of potting mix weighs 20 to 40 lb. The weight comes from volume times bulk density. Check the material name and the density first, and use the Topsoil Weight to Cubic Feet Calculator for your own bag.