78 lb works out to 1x10 + 1x5 per side plus the bar — call it 75 lb in practice, since gyms rarely stock the odd change. 6 reps sits comfortably inside the 2-to-10 range these formulas were fitted on, so this estimate is about as reliable as the method gets. Your 65 lb set represents about 83% of the estimated max.
How far 78 lb can be trusted
Six reps is where the equations start to separate. The 4 lb between 75 and 79 lb is wider than the same lifter would see from a triple, because past five reps the different curve shapes behind each formula begin to matter. Conditioning also starts to leak into the answer: a six-rep set asks something of your work capacity that a single does not, and lifters who are strong but poorly conditioned come out under-estimated here.
Training loads from a 78 lb max
Programmes are written as percentages of the max, not as absolute weights. From 78 lb, to the nearest pound, because 5 lb steps collapse into each other at this load:
| Percentage | Load | Typical set |
|---|---|---|
| 95% | 74 lb | Heavy single |
| 90% | 70 lb | Doubles and triples |
| 85% | 66 lb | Sets of four to five |
| 80% | 62 lb | Sets of six |
| 75% | 58 lb | Sets of eight |
| 70% | 55 lb | Volume work, ten or more |
At this end of the rack almost none of those percentages lands on a plate you own. 78 lb itself builds as 1x10 + 1x5 per side plus the bar, which is 75 lb — near enough, and the miss is smaller than the 4 lb the seven formulas disagree by. This is the weight range where a pair of 2.5 lb or 1.25 lb plates genuinely earns its place, because a 10 lb jump here is a much larger proportional step than it is at 300.
The formulas behind this answer, and their limitations
The table above the fold is Epley (1985), Brzycki (1993), Lombardi (1989), O'Conner (1989), Wathan (1994), Lander (1985) and Mayhew (1992), each applied to 65 lb for 6 reps; the headline figure is their median. All seven assume a set taken close to failure with clean technique. At 6 reps you are still inside the fitted band, but conditioning is now affecting the result alongside strength, and the seven have begun to curve away from each other. They also under-rate strong, experienced lifters, who hold a higher percentage of max at any rep count than the regression average. The full account — the populations behind each equation, what a bounced rep does to it, and why we stop at ten reps — is set out on the methodology page. Warm up thoroughly and use safety bars or a spotter before going anywhere near 78 lb. This is a training estimate, not medical advice.