Backpacks and water canisters: how to pick improvised weights

You have no dumbbells, and you want squats and rows to stop being bodyweight exercises. A rucksack full of books and a canister of water are the closest things in the flat. They genuinely work — but only if the bag and the container survive what you plan to do with them, and only if you know how much you are actually lifting.

This is not a list of exercises. It is a guide to looking at the rucksack you already own, or the one you are thinking of buying, and judging whether it can serve as a weight — what you gain, and where improvising really runs out.

What an improvised weight has to have

A known load. If you cannot name the number, you are guessing rather than progressing. Water solves this neatly: one litre is one kilogram, so a full 10-litre canister is exactly 10 kg with no scales involved. Books are the opposite — the bag means nothing until you have stood on the bathroom scales holding it.

Contents that stay put. A load that slides mid-set shifts its centre of gravity and turns the exercise into a balance drill. For strength work you want a dead, solid parcel.

A grip that fails after the muscles, not before. With most improvised loads the fingers give out long before the legs or back do. That is the single most common reason people conclude a rucksack "doesn't work".

The fourth requirement is less obvious: being able to change the load in small steps. Jumping from 10 kg to 20 kg is too much for anyone. Water gives you two-litre increments, which is about right. If picking a starting load feels vague, the reasoning in how to choose the weight for your first set without guessing transfers directly.

The specs that matter and what each one tells you

Load rating and where the strap meets the bag

The fabric almost never tears first. What fails is the seam where the shoulder strap joins the body of the pack, or a plastic buckle on the chest strap. Load the bag, lift it by one strap and look at that junction: if the stitching fans out under tension, that is your ceiling.

As a rough guide, ordinary daypacks and school bags carry about 10–12 kg comfortably and should be left there. Hiking packs with reinforced anchor points, double stitching and a hip belt handle 20–25 kg because that is what they were built for. The spread depends on fabric weight, how many rows of stitching hold the strap, and whether there is a frame passing part of the load onto your hips instead of your shoulders.

Density: how many kilos actually fit

Litres tell you nothing until you decide on the filling. Water is about 1 kg per litre. Dry sand runs roughly 1.4–1.6 kg per litre, so the same space carries nearly twice as much. Books, because of the air gaps between them, work out around 0.5–0.7 kg per litre in practice.

In real terms: a 25–30 litre rucksack packed with books rarely passes 15–20 kg. The same pack filled with sand would blow past the seam limit long before it was full. That is the useful conclusion — with sand the bag limits you, with books the volume does.

Grip

A comfortable handle is somewhere around 25–35 mm thick. Canister handles are usually thinner, with a sharp moulded edge that digs into the fingers after about thirty seconds. Wrap the handle in a cloth and tape and you buy yourself several more reps before the hand quits.

With a rucksack the grip depends on the movement: held against the chest for goblet squats you are gripping the straps, so wide, firm straps beat thin slippery ones.

How stable the contents are

Water in a half-empty canister sloshes and drags the load around. That is not always a flaw — for carries, lunges and anti-rotation work an unstable load is arguably more useful. For clean strength work you want the container filled to the brim with no air in it.

Pack books flat against the back panel and stuff towels into the gaps. The aim is a load sitting high and close to the spine rather than hanging low and pulling you backwards.

Materials and small parts

For the container: thick plastic, a screw cap that does not weep, and a handle moulded into the body rather than glued on. Glass is out. So are drawstring bags — the cord snaps at the worst moment.

For the pack: denser fabric, buckles that do not crack in the cold, and a hip belt if you are going to walk under the load. If you are also building a push-up progression around this, what is actually worth buying for push-up progressions covers the pieces that pair well with it.

Space and money, realistically

Space is the easy part. A 20-litre canister takes up about the footprint of a sheet of paper and lives in a corner or under a desk. The rucksack hangs on a door. For the training itself you need a rectangle of roughly 2 x 1.5 m, plus headroom if you press overhead. If you are planning further ahead, how much floor space and ceiling height a home gym really needs is worth a read.

Money is the whole point of this approach. Canisters are usually already in the house, and a bag of sand or fine gravel is among the cheapest things you can buy per kilogram of load. The full kit — canister, sand, strong tape, a couple of tough bags — typically costs less than one single barbell plate.

The range depends on whether you already own a decent rucksack (the expensive item), whether you fill with water or sand, and how many extras like compression straps you add. Once you start buying purpose-made weighted bags with handles, the price climbs towards real equipment, and at that point the fair comparison is with dumbbells rather than with improvising.

Common mistakes

• Filling the pack to its seam limit on day one. Start at half and watch how the stitching behaves over a few weeks.
• Not knowing the number. Without weighing it you have movement, not training.
• A part-full canister. The water inside becomes a wrecking ball that pulls you off line.
• Dumping the pack on the floor with a jerk and a rounded back. Most injuries here happen between sets, not during them.
• Training on a hard floor above neighbours. If that is your situation, see how to train with weights in a flat without the noise.
• Stalling. When the pack maxes out at 20 kg and you are doing twenty easy reps, the kit has become the limiting factor.

Who it suits and who it doesn't

It suits beginners for the first few months, people who travel often, and anyone training in a flat with nowhere to store kit. For goblet squats at 3 x 10–15, rows at 3 x 8–12, Romanian deadlifts and carries of 3–4 x 30–40 m, a rucksack and a canister do a perfectly legitimate job.

It does not suit you if you already squat 20 kg for fifteen solid reps, because there is no safe way to add the next five. It also fails for heavy overhead pressing, where the grip is unreliable, and for anything where dropping the load would be dangerous.

At that point the answer is not a bigger bag but adjustable load, and the buying order is worth thinking through in advance — which pieces to buy first for a small gym lays out a sequence that makes sense.

When to see a doctor

Stop and speak to a doctor or physiotherapist if carrying load gives you sharp low back pain, any numbness or weakness in a leg or arm, or shoulder pain that lasts more than two weeks and does not settle with rest. The same applies if you have a hernia, uncontrolled high blood pressure, or previous disc surgery — in those cases agree what you are allowed to carry before you put twenty kilos on your back.

In short

Water gives you an exact number and small increments, sand gives you density, books give you whatever is on the shelf. The rucksack is the weak link: roughly 10–12 kg for an ordinary one, 20–25 kg for a hiking pack. Weigh the load, fill containers to the top, wrap the handles and mind how you set it down. And when 20 kg starts to feel light, that is not improvising failing — it is you having taken everything it had.